Shoujin Sun - Profile on Academia.edu (original) (raw)

Papers by Shoujin Sun

Laser cladding (LC) was used to investigate the repair of high strength steel in aircraft applica... more Laser cladding (LC) was used to investigate the repair of high strength steel in aircraft applications, such as landing gears. This paper reports on the microstructure and microhardness properties of the deposited AISI 4340 clad layer on AISI 4340 steel substrate. Microhardness results showed the clad layer was 30-40% harder than the base material. Stress relieving the clad allowed the clad and HAZ areas to soften 10% below the base material. High dilution provided a favorable result on the hardness at the interface.

Mechanical properties of selective laser melted Ti-6Al-4V with different layer thickness

International Congress on Applications of Lasers & Electro-Optics, 2014

Laser-based metal deposition process such as selective laser melting (SLM) is one of Direct Metal... more Laser-based metal deposition process such as selective laser melting (SLM) is one of Direct Metal Deposition (DMD) or Additive Manufacturing (AM) processes. Due to the nature of its layer-by-layer process, the microstructures from the bottom layers to the top layers are significantly different due to highly thermal gradient induced by laser beam combined with different cooling rates at each built layer. The SLM process parameters such as laser power, scan speed, layer thickness, hatch spacing etc have a major influence on the mechanical properties of the material fabricated. The relationship between mechanical properties associated with microstructure and process parameters is critical for the manufacture of functional components. The understanding of this relationship will help to facilitate future studies on manufacture and repair of titanium alloy parts/components with SLM technology. Increase in layer thickness will lead to increase in productivity. However, such an increase may impact on the mechanical properties of the material.This paper presents the effect of powder layer thickness on the mechanical properties (tensile and fatigue) of manufactured specimens. The experimental results in this investigation showed that the increase in layer thickness from 30 to 90 µm did not affect the tensile strengths but the ductility was dramatically reduced. The fatigue life was also significantly decreased. The results indicate that the SLM process needs to be optimised for a thicker powder layer case.Laser-based metal deposition process such as selective laser melting (SLM) is one of Direct Metal Deposition (DMD) or Additive Manufacturing (AM) processes. Due to the nature of its layer-by-layer process, the microstructures from the bottom layers to the top layers are significantly different due to highly thermal gradient induced by laser beam combined with different cooling rates at each built layer. The SLM process parameters such as laser power, scan speed, layer thickness, hatch spacing etc have a major influence on the mechanical properties of the material fabricated. The relationship between mechanical properties associated with microstructure and process parameters is critical for the manufacture of functional components. The understanding of this relationship will help to facilitate future studies on manufacture and repair of titanium alloy parts/components with SLM technology. Increase in layer thickness will lead to increase in productivity. However, such an increase may impact on the mechanic...

Mechanical properties of Ti6Al4V and AlSi12Mg lattice structures manufactured by Selective Laser Melting (SLM)

Laser Additive Manufacturing, 2017

Emerging additive manufacturing (AM) techniques such as selective laser melting (SLM) present an ... more Emerging additive manufacturing (AM) techniques such as selective laser melting (SLM) present an exceptional opportunity for the manufacture of lattice structures which exhibit attractive mechanical properties beyond the capabilities of solid materials. However, to apply SLM-manufactured lattices as structural elements, it is necessary to quantify their manufacturability as well as key mechanical properties, such as compressive strength and stiffness, under varying material, geometric and loading conditions. This work reports on the experimental investigation of the SLM manufacturability and mechanical properties of titanium (Ti6Al4V) and aluminium (AlSi12Mg) alloy lattice structures; the materials were selected because of their inherently high specific strength (pursuant to lattice structure design opportunities) and compatibility with SLM. A range of lattice structures are manufactured and experimentally assessed for compressive strength and stiffness, with varying materials, cell topology, cell size, number of unit cells and associated boundary conditions. The mechanical properties as well as deformation and failure characteristics are analyzed and compared with theoretically predicted behaviour.

Materials, Aug 17, 2022

Powder bed fusion with laser beam of metals (PBF-LB/M) is a widely used technology to produce par... more Powder bed fusion with laser beam of metals (PBF-LB/M) is a widely used technology to produce parts with a high freedom in design paired with excellent mechanical properties. The casting alloy AlSi10Mg features a wide process window and a microstructure with excellent mechanical properties which are not obtainable through conventional manufacturing. One possibility for achieving this is by influencing the solidification which then directly affects the local part properties. In this study, the effect of different laser beam profiles with gaussian and top-hat intensity distributions, as well as the influence of varying parameter sets on the microstructure and microhardness within the same specimen, was examined. A test specimen consisting of many small cubes was built with different parameters. It was found that the local properties can be varied in a wide range. Build-height-dependent in-situ aging effects can thereby be exploited for tailoring the local material properties. Thus, an extra degree of freedom is added to the design of additively manufactured parts.

Advanced Engineering Materials, 2018

Metal additive manufacturing (AM) is an innovative manufacturing technique, which builds parts in... more Metal additive manufacturing (AM) is an innovative manufacturing technique, which builds parts incrementally layer by layer. Thus, metal AM has inherent advantages in part complexity, time, and waste saving. However, due to its complex thermal cycle and rapid solidification during processing, the alloys well suit and commercially used for metal AM today are limited. Therefore, it is important to understand the alloying strategy and current progress with materials performance to consider alloy development for metal AM. This review presents the current range of alloys available for metal AM, including titanium, steel, nickel, aluminum, less common alloys (including Mg alloys, metal matrix composites alloys, and low melting point alloys), and compositionally complex alloys (including bulk metallic glasses and high entropy alloys) with a focus on the relationship between compositions, processing, microstructures, and properties of each alloy system. In addition, some promising alloy systems for metal AM are highlighted. Approaches for designing and optimizing new materials for metal AM have been summarized.

The Microstructure and Mechanical Properties of As-rolled Dual Phase Steel: Part II - Mechanical Properties

The influence of pre-annealing and post-annealing heat treatments on the tensile properties of du... more The influence of pre-annealing and post-annealing heat treatments on the tensile properties of dual phase steel has been investigated. Post-annealing lowers the tensile strength and increases the % elongation by decreasing the aspect ratio of the fibrous martensite. The asrolled steel shows a 'delamination-type' fracture whereas the post-annealed steel does not. The tensile strength of these partitioned and fibrous steels are compared with Mileiko's theory for plastic instability in ductile composites.

Powder Bed Fusion Processes

Additive Manufacturing Technologies, 2015

Powder bed fusion (PBF) processes were among the first commercialized AM processes. Developed at ... more Powder bed fusion (PBF) processes were among the first commercialized AM processes. Developed at the University of Texas at Austin, USA, Selective Laser Sintering (SLS) was the first commercialized powder bed fusion process. Its basic method of operation is schematically shown in Fig. 5.1, and all other PBF processes modify this basic approach in one or more ways to enhance machine productivity, enable different materials to be processed, and/or to avoid specific patented features.

Metals

With the advent of additive manufacturing as an advanced technology for the fabrication of titani... more With the advent of additive manufacturing as an advanced technology for the fabrication of titanium components, there is a pressing need to investigate the machinability of parts produced using these techniques compared to components made with conventional wrought methodologies. The motivation for this study was to investigate the influences of machining parameters, especially cutting depth, on the machinability of selective laser melted (SLMed) Ti6Al4V tubes, by analyzing the cutting responses, including cutting forces, machined surface roughness and tool wear at varying cutting parameters. Generally, it can be inferred that specific cutting tools used to machine wrought titanium components can also be used for SLMed parts when carrying out finish-machining operations. Cutting forces in the machining of SLMed workpieces could be up to 70% higher than those in machining the wrought counterparts. In contrast, the tool-wear analysis correspondingly showed larger tool-workpiece engagem...

Mechanical properties and deformation mechanisms of martensitic Ti6Al4V alloy processed by laser powder bed fusion and water quenching

Materials Science and Engineering: A, 2022

Laser beam shaping and surface treatment of Ze41A-T5 magnesium alloy

Materials, 2020

Additive manufacturing facilitates the design of porous metal implants with detailed internal arc... more Additive manufacturing facilitates the design of porous metal implants with detailed internal architecture. A rationally designed porous structure can provide to biocompatible titanium alloys biomimetic mechanical and biological properties for bone regeneration. However, increased porosity results in decreased material strength. The porosity and pore sizes that are ideal for porous implants are still controversial in the literature, complicating the justification of a design decision. Recently, metallic porous biomaterials have been proposed for load-bearing applications beyond surface coatings. This recent science lacks standards, but the Quality by Design (QbD) system can assist the design process in a systematic way. This study used the QbD system to explore the Quality Target Product Profile and Ideal Quality Attributes of additively manufactured titanium porous scaffolds for bone regeneration with a biomimetic approach. For this purpose, a total of 807 experimental results extr...

International Journal of Extreme Manufacturing, 2021

Several detailed studies have comprehensively investigated the benefits and limitations of laser-... more Several detailed studies have comprehensively investigated the benefits and limitations of laser-assisted machining (LAM) of titanium alloys. These studies have highlighted the positive impact of the application of laser preheating on reducing cutting forces and improving productivity but have also identified the detrimental effect of LAM on tool life. This paper seeks to evaluate a series of the most common cutting tools with different coating types used in the machining of titanium alloys to identify whether coating type has a dramatic effect on the dominant tool wear mechanisms active during the process. The findings provide a clear illustration that the challenges facing the application of LAM are associated with the development of new types of cutting tools which are not subjected to the diffusion-controlled wear processes that dominate the performance of current cutting tools.

Tool wear mechanisms involved in crater formation on uncoated carbide tool when machining Ti6Al4V alloy

The International Journal of Advanced Manufacturing Technology, 2015

When machining titanium alloys at cutting speeds higher than 60 m/min using cemented carbide cutt... more When machining titanium alloys at cutting speeds higher than 60 m/min using cemented carbide cutting tools, the tool wears out rapidly. With the ever-increasing use of titanium alloys, it is essential to address this issue of rapid tool wear in order to reduce manufacturing costs. Therefore, the intention of this study was to investigate all possible tool wear mechanisms involved when using uncoated carbide cutting tools to machine Ti6Al4V titanium alloy at a cutting speed of 150 m/min under dry cutting conditions. Adhesion, diffusion, attrition, and abrasion were found to be the mechanisms associated with the cratering of the rake surface of the cutting tool. The plastic deformation of the cutting edge was also noticed which resulted in weakening of the rake surface and clear evidence has been presented. Based on this evidence, the process of the formation of the crater wear has been described in detail.

Microstructure and hardness characterisation of laser coatings produced with a mixture of AISI 420 stainless steel and Fe-C-Cr-Nb-B-Mo steel alloy powders

Surface and Coatings Technology, 2016

Fe-C-Cr-Nb-B-Mo alloy powder and AISI 420 SS powder are deposited using laser cladding to increas... more Fe-C-Cr-Nb-B-Mo alloy powder and AISI 420 SS powder are deposited using laser cladding to increase the hardness for wear resistant applications. Mixtures from 0 to 100 wt.% were evaluated to understand the effect on the elemental composition, microstructure, phases, and microhardness. The mixture of carbon, boron and niobium in the Fe-C-Cr-Nb-B-Mo alloy powder introduces complex carbides into a Fe-based matrix of AISI 420 SS which increases its hardness. Hardness increased linearly with increasing Fe-C-Cr-Nb-B-Mo alloy, but substantial micro-cracking was observed in the clad layer at additions of 60 wt.% and above; related to a transition from a hypoeutectic alloy containing α-Fe/α' dendrites with an (Fe,Cr)2B and γ-Fe eutectic to primary and continuous carbo-borides M2B (where M represents Fe and Cr) and M23(B,C)6 carbides (where M represents Fe, Cr, Mo) with MC particles (where M represents Nb and Mo). The highest average hardness, for an alloy without micro-cracking, of 952 HV was observed in a 40 wt.% alloy. High stress abrasive scratch testing was conducted on all alloys at various loads (500, 1500, 2500 N). Alloy content was found to have a strong effect on the wear mode and the abrasive wear rate, and the presence of micro-cracks was detrimental to abrasive wear resistance.

The aim of this work is to develop a 3-D transient finite element model for a moving Gaussian las... more The aim of this work is to develop a 3-D transient finite element model for a moving Gaussian laser heat source to predict the depth of the heat-affected zone (HAZ) and temperature distribution in a Ti6Al4V alloy workpiece. It is found that the temperature profile and depth of HAZ are strongly dependent on the parameters of the laser beam. The thermal model simulations are compared with results produced by experimental work and these show close agreement. Introduction Titanium alloys have been widely used in the aerospace, biomedical and automotive industries because of their high strength-to-weight ratio and superior corrosion resistance. However, it is very difficult to machine these alloys due to their poor machinability [1]. Laser assisted machining (LAM) is a new and innovative manufacturing process that has been investigated as an alternative to conventional machining of hard and/or difficult-to-process materials such as titanium alloys [2-7]. This heat-assisted process induce...

Metals

New metastable β titanium alloys are receiving increasing attention due to their excellent biomec... more New metastable β titanium alloys are receiving increasing attention due to their excellent biomechanical properties and machinability is critical to their uptake. In this study, machining chip microstructure has been investigated to gain an understanding of strain and temperature fields during cutting. For higher cutting speeds, ≥60 m/min, the chips have segmented morphologies characterised by a serrated appearance. High levels of strain in the primary shear zone promote formation of expanded shear band regions between segments which exhibit intensive refinement of the β phase down to grain sizes below 100 nm. The presence of both α and β phases across the expanded shear band suggests that temperatures during cutting are in the range of 400–600 °C. For the secondary shear zone, very large strains at the cutting interface result in heavily refined and approximately equiaxed nanocrystalline β grains with sizes around 20–50 nm, while further from the interface the β grains become highl...

Effect of laser beam on the chip formation in machining of titanium alloys

International Congress on Applications of Lasers & Electro-Optics

Effect of tool wear evolution on chip formation during dry machining of Ti-6Al-4V alloy

International Journal of Machine Tools and Manufacture

Pacific International Conference on Applications of Lasers and Optics

The melt pool temperature in pulsed laser cladding of stellite 6 was measured with a two-colour p... more The melt pool temperature in pulsed laser cladding of stellite 6 was measured with a two-colour pyrometer. The pulse peak temperature (p T), durations when the melt and continuous wave (CW) laser cladding of stellite 6. Comparison between the experimental data and prediction has been made. Thick clad layer with low level of dilution requires higher value of the product of f t 1 ⋅ , longer beam interaction time (τ) and large M D .

New metastable β titanium alloys are receiving increasing attention due to their excellent biomec... more New metastable β titanium alloys are receiving increasing attention due to their excellent biomechanical properties and machinability is critical to their uptake. In this study machining chip microstructure have been investigated to gain an understanding of strain and temperature fields during cutting. For higher cutting speeds, ≥60 m/min, the chips have segmented morphologies characterised by a serrated appearance. High levels of strain in the primary shear zone promote formation of expanded shear band regions between segments which exhibit intensive refinement of the β phase down to grain sizes below 100 nm. The presence of both α and β phases across the expanded shear band suggests that temperatures during cutting are in the range of 400-600°C. For the secondary shear zone, very large strains at the cutting interface result in heavily refined and approximately equiaxed nanocrystalline β grains with sizes around 20-50 nm, while further from the interface the β grains become highly elongated in the shear direction. An absence of the α phase in the region immediately adjacent to the cutting interface indicates recrystallization during cutting and temperatures in excess of the 720°C β transus temperature.

Laser cladding (LC) was used to investigate the repair of high strength steel in aircraft applica... more Laser cladding (LC) was used to investigate the repair of high strength steel in aircraft applications, such as landing gears. This paper reports on the microstructure and microhardness properties of the deposited AISI 4340 clad layer on AISI 4340 steel substrate. Microhardness results showed the clad layer was 30-40% harder than the base material. Stress relieving the clad allowed the clad and HAZ areas to soften 10% below the base material. High dilution provided a favorable result on the hardness at the interface.

Mechanical properties of selective laser melted Ti-6Al-4V with different layer thickness

International Congress on Applications of Lasers & Electro-Optics, 2014

Laser-based metal deposition process such as selective laser melting (SLM) is one of Direct Metal... more Laser-based metal deposition process such as selective laser melting (SLM) is one of Direct Metal Deposition (DMD) or Additive Manufacturing (AM) processes. Due to the nature of its layer-by-layer process, the microstructures from the bottom layers to the top layers are significantly different due to highly thermal gradient induced by laser beam combined with different cooling rates at each built layer. The SLM process parameters such as laser power, scan speed, layer thickness, hatch spacing etc have a major influence on the mechanical properties of the material fabricated. The relationship between mechanical properties associated with microstructure and process parameters is critical for the manufacture of functional components. The understanding of this relationship will help to facilitate future studies on manufacture and repair of titanium alloy parts/components with SLM technology. Increase in layer thickness will lead to increase in productivity. However, such an increase may impact on the mechanical properties of the material.This paper presents the effect of powder layer thickness on the mechanical properties (tensile and fatigue) of manufactured specimens. The experimental results in this investigation showed that the increase in layer thickness from 30 to 90 µm did not affect the tensile strengths but the ductility was dramatically reduced. The fatigue life was also significantly decreased. The results indicate that the SLM process needs to be optimised for a thicker powder layer case.Laser-based metal deposition process such as selective laser melting (SLM) is one of Direct Metal Deposition (DMD) or Additive Manufacturing (AM) processes. Due to the nature of its layer-by-layer process, the microstructures from the bottom layers to the top layers are significantly different due to highly thermal gradient induced by laser beam combined with different cooling rates at each built layer. The SLM process parameters such as laser power, scan speed, layer thickness, hatch spacing etc have a major influence on the mechanical properties of the material fabricated. The relationship between mechanical properties associated with microstructure and process parameters is critical for the manufacture of functional components. The understanding of this relationship will help to facilitate future studies on manufacture and repair of titanium alloy parts/components with SLM technology. Increase in layer thickness will lead to increase in productivity. However, such an increase may impact on the mechanic...

Mechanical properties of Ti6Al4V and AlSi12Mg lattice structures manufactured by Selective Laser Melting (SLM)

Laser Additive Manufacturing, 2017

Emerging additive manufacturing (AM) techniques such as selective laser melting (SLM) present an ... more Emerging additive manufacturing (AM) techniques such as selective laser melting (SLM) present an exceptional opportunity for the manufacture of lattice structures which exhibit attractive mechanical properties beyond the capabilities of solid materials. However, to apply SLM-manufactured lattices as structural elements, it is necessary to quantify their manufacturability as well as key mechanical properties, such as compressive strength and stiffness, under varying material, geometric and loading conditions. This work reports on the experimental investigation of the SLM manufacturability and mechanical properties of titanium (Ti6Al4V) and aluminium (AlSi12Mg) alloy lattice structures; the materials were selected because of their inherently high specific strength (pursuant to lattice structure design opportunities) and compatibility with SLM. A range of lattice structures are manufactured and experimentally assessed for compressive strength and stiffness, with varying materials, cell topology, cell size, number of unit cells and associated boundary conditions. The mechanical properties as well as deformation and failure characteristics are analyzed and compared with theoretically predicted behaviour.

Materials, Aug 17, 2022

Powder bed fusion with laser beam of metals (PBF-LB/M) is a widely used technology to produce par... more Powder bed fusion with laser beam of metals (PBF-LB/M) is a widely used technology to produce parts with a high freedom in design paired with excellent mechanical properties. The casting alloy AlSi10Mg features a wide process window and a microstructure with excellent mechanical properties which are not obtainable through conventional manufacturing. One possibility for achieving this is by influencing the solidification which then directly affects the local part properties. In this study, the effect of different laser beam profiles with gaussian and top-hat intensity distributions, as well as the influence of varying parameter sets on the microstructure and microhardness within the same specimen, was examined. A test specimen consisting of many small cubes was built with different parameters. It was found that the local properties can be varied in a wide range. Build-height-dependent in-situ aging effects can thereby be exploited for tailoring the local material properties. Thus, an extra degree of freedom is added to the design of additively manufactured parts.

Advanced Engineering Materials, 2018

Metal additive manufacturing (AM) is an innovative manufacturing technique, which builds parts in... more Metal additive manufacturing (AM) is an innovative manufacturing technique, which builds parts incrementally layer by layer. Thus, metal AM has inherent advantages in part complexity, time, and waste saving. However, due to its complex thermal cycle and rapid solidification during processing, the alloys well suit and commercially used for metal AM today are limited. Therefore, it is important to understand the alloying strategy and current progress with materials performance to consider alloy development for metal AM. This review presents the current range of alloys available for metal AM, including titanium, steel, nickel, aluminum, less common alloys (including Mg alloys, metal matrix composites alloys, and low melting point alloys), and compositionally complex alloys (including bulk metallic glasses and high entropy alloys) with a focus on the relationship between compositions, processing, microstructures, and properties of each alloy system. In addition, some promising alloy systems for metal AM are highlighted. Approaches for designing and optimizing new materials for metal AM have been summarized.

The Microstructure and Mechanical Properties of As-rolled Dual Phase Steel: Part II - Mechanical Properties

The influence of pre-annealing and post-annealing heat treatments on the tensile properties of du... more The influence of pre-annealing and post-annealing heat treatments on the tensile properties of dual phase steel has been investigated. Post-annealing lowers the tensile strength and increases the % elongation by decreasing the aspect ratio of the fibrous martensite. The asrolled steel shows a 'delamination-type' fracture whereas the post-annealed steel does not. The tensile strength of these partitioned and fibrous steels are compared with Mileiko's theory for plastic instability in ductile composites.

Powder Bed Fusion Processes

Additive Manufacturing Technologies, 2015

Powder bed fusion (PBF) processes were among the first commercialized AM processes. Developed at ... more Powder bed fusion (PBF) processes were among the first commercialized AM processes. Developed at the University of Texas at Austin, USA, Selective Laser Sintering (SLS) was the first commercialized powder bed fusion process. Its basic method of operation is schematically shown in Fig. 5.1, and all other PBF processes modify this basic approach in one or more ways to enhance machine productivity, enable different materials to be processed, and/or to avoid specific patented features.

Metals

With the advent of additive manufacturing as an advanced technology for the fabrication of titani... more With the advent of additive manufacturing as an advanced technology for the fabrication of titanium components, there is a pressing need to investigate the machinability of parts produced using these techniques compared to components made with conventional wrought methodologies. The motivation for this study was to investigate the influences of machining parameters, especially cutting depth, on the machinability of selective laser melted (SLMed) Ti6Al4V tubes, by analyzing the cutting responses, including cutting forces, machined surface roughness and tool wear at varying cutting parameters. Generally, it can be inferred that specific cutting tools used to machine wrought titanium components can also be used for SLMed parts when carrying out finish-machining operations. Cutting forces in the machining of SLMed workpieces could be up to 70% higher than those in machining the wrought counterparts. In contrast, the tool-wear analysis correspondingly showed larger tool-workpiece engagem...

Mechanical properties and deformation mechanisms of martensitic Ti6Al4V alloy processed by laser powder bed fusion and water quenching

Materials Science and Engineering: A, 2022

Laser beam shaping and surface treatment of Ze41A-T5 magnesium alloy

Materials, 2020

Additive manufacturing facilitates the design of porous metal implants with detailed internal arc... more Additive manufacturing facilitates the design of porous metal implants with detailed internal architecture. A rationally designed porous structure can provide to biocompatible titanium alloys biomimetic mechanical and biological properties for bone regeneration. However, increased porosity results in decreased material strength. The porosity and pore sizes that are ideal for porous implants are still controversial in the literature, complicating the justification of a design decision. Recently, metallic porous biomaterials have been proposed for load-bearing applications beyond surface coatings. This recent science lacks standards, but the Quality by Design (QbD) system can assist the design process in a systematic way. This study used the QbD system to explore the Quality Target Product Profile and Ideal Quality Attributes of additively manufactured titanium porous scaffolds for bone regeneration with a biomimetic approach. For this purpose, a total of 807 experimental results extr...

International Journal of Extreme Manufacturing, 2021

Several detailed studies have comprehensively investigated the benefits and limitations of laser-... more Several detailed studies have comprehensively investigated the benefits and limitations of laser-assisted machining (LAM) of titanium alloys. These studies have highlighted the positive impact of the application of laser preheating on reducing cutting forces and improving productivity but have also identified the detrimental effect of LAM on tool life. This paper seeks to evaluate a series of the most common cutting tools with different coating types used in the machining of titanium alloys to identify whether coating type has a dramatic effect on the dominant tool wear mechanisms active during the process. The findings provide a clear illustration that the challenges facing the application of LAM are associated with the development of new types of cutting tools which are not subjected to the diffusion-controlled wear processes that dominate the performance of current cutting tools.

Tool wear mechanisms involved in crater formation on uncoated carbide tool when machining Ti6Al4V alloy

The International Journal of Advanced Manufacturing Technology, 2015

When machining titanium alloys at cutting speeds higher than 60 m/min using cemented carbide cutt... more When machining titanium alloys at cutting speeds higher than 60 m/min using cemented carbide cutting tools, the tool wears out rapidly. With the ever-increasing use of titanium alloys, it is essential to address this issue of rapid tool wear in order to reduce manufacturing costs. Therefore, the intention of this study was to investigate all possible tool wear mechanisms involved when using uncoated carbide cutting tools to machine Ti6Al4V titanium alloy at a cutting speed of 150 m/min under dry cutting conditions. Adhesion, diffusion, attrition, and abrasion were found to be the mechanisms associated with the cratering of the rake surface of the cutting tool. The plastic deformation of the cutting edge was also noticed which resulted in weakening of the rake surface and clear evidence has been presented. Based on this evidence, the process of the formation of the crater wear has been described in detail.

Microstructure and hardness characterisation of laser coatings produced with a mixture of AISI 420 stainless steel and Fe-C-Cr-Nb-B-Mo steel alloy powders

Surface and Coatings Technology, 2016

Fe-C-Cr-Nb-B-Mo alloy powder and AISI 420 SS powder are deposited using laser cladding to increas... more Fe-C-Cr-Nb-B-Mo alloy powder and AISI 420 SS powder are deposited using laser cladding to increase the hardness for wear resistant applications. Mixtures from 0 to 100 wt.% were evaluated to understand the effect on the elemental composition, microstructure, phases, and microhardness. The mixture of carbon, boron and niobium in the Fe-C-Cr-Nb-B-Mo alloy powder introduces complex carbides into a Fe-based matrix of AISI 420 SS which increases its hardness. Hardness increased linearly with increasing Fe-C-Cr-Nb-B-Mo alloy, but substantial micro-cracking was observed in the clad layer at additions of 60 wt.% and above; related to a transition from a hypoeutectic alloy containing α-Fe/α' dendrites with an (Fe,Cr)2B and γ-Fe eutectic to primary and continuous carbo-borides M2B (where M represents Fe and Cr) and M23(B,C)6 carbides (where M represents Fe, Cr, Mo) with MC particles (where M represents Nb and Mo). The highest average hardness, for an alloy without micro-cracking, of 952 HV was observed in a 40 wt.% alloy. High stress abrasive scratch testing was conducted on all alloys at various loads (500, 1500, 2500 N). Alloy content was found to have a strong effect on the wear mode and the abrasive wear rate, and the presence of micro-cracks was detrimental to abrasive wear resistance.

The aim of this work is to develop a 3-D transient finite element model for a moving Gaussian las... more The aim of this work is to develop a 3-D transient finite element model for a moving Gaussian laser heat source to predict the depth of the heat-affected zone (HAZ) and temperature distribution in a Ti6Al4V alloy workpiece. It is found that the temperature profile and depth of HAZ are strongly dependent on the parameters of the laser beam. The thermal model simulations are compared with results produced by experimental work and these show close agreement. Introduction Titanium alloys have been widely used in the aerospace, biomedical and automotive industries because of their high strength-to-weight ratio and superior corrosion resistance. However, it is very difficult to machine these alloys due to their poor machinability [1]. Laser assisted machining (LAM) is a new and innovative manufacturing process that has been investigated as an alternative to conventional machining of hard and/or difficult-to-process materials such as titanium alloys [2-7]. This heat-assisted process induce...

Metals

New metastable β titanium alloys are receiving increasing attention due to their excellent biomec... more New metastable β titanium alloys are receiving increasing attention due to their excellent biomechanical properties and machinability is critical to their uptake. In this study, machining chip microstructure has been investigated to gain an understanding of strain and temperature fields during cutting. For higher cutting speeds, ≥60 m/min, the chips have segmented morphologies characterised by a serrated appearance. High levels of strain in the primary shear zone promote formation of expanded shear band regions between segments which exhibit intensive refinement of the β phase down to grain sizes below 100 nm. The presence of both α and β phases across the expanded shear band suggests that temperatures during cutting are in the range of 400–600 °C. For the secondary shear zone, very large strains at the cutting interface result in heavily refined and approximately equiaxed nanocrystalline β grains with sizes around 20–50 nm, while further from the interface the β grains become highl...

Effect of laser beam on the chip formation in machining of titanium alloys

International Congress on Applications of Lasers & Electro-Optics

Effect of tool wear evolution on chip formation during dry machining of Ti-6Al-4V alloy

International Journal of Machine Tools and Manufacture

Pacific International Conference on Applications of Lasers and Optics

The melt pool temperature in pulsed laser cladding of stellite 6 was measured with a two-colour p... more The melt pool temperature in pulsed laser cladding of stellite 6 was measured with a two-colour pyrometer. The pulse peak temperature (p T), durations when the melt and continuous wave (CW) laser cladding of stellite 6. Comparison between the experimental data and prediction has been made. Thick clad layer with low level of dilution requires higher value of the product of f t 1 ⋅ , longer beam interaction time (τ) and large M D .

New metastable β titanium alloys are receiving increasing attention due to their excellent biomec... more New metastable β titanium alloys are receiving increasing attention due to their excellent biomechanical properties and machinability is critical to their uptake. In this study machining chip microstructure have been investigated to gain an understanding of strain and temperature fields during cutting. For higher cutting speeds, ≥60 m/min, the chips have segmented morphologies characterised by a serrated appearance. High levels of strain in the primary shear zone promote formation of expanded shear band regions between segments which exhibit intensive refinement of the β phase down to grain sizes below 100 nm. The presence of both α and β phases across the expanded shear band suggests that temperatures during cutting are in the range of 400-600°C. For the secondary shear zone, very large strains at the cutting interface result in heavily refined and approximately equiaxed nanocrystalline β grains with sizes around 20-50 nm, while further from the interface the β grains become highly elongated in the shear direction. An absence of the α phase in the region immediately adjacent to the cutting interface indicates recrystallization during cutting and temperatures in excess of the 720°C β transus temperature.