Malki Pinkas - Profile on Academia.edu (original) (raw)

Papers by Malki Pinkas

Analele Universităţii "Dunărea de Jos" din Galaţi, Dec 28, 2018

In today's additive manufacturing sector, one of the most popular areas is selective laser meltin... more In today's additive manufacturing sector, one of the most popular areas is selective laser melting (SLM) due to its capability of producing geometrically complex metal parts directly from CAD model in a few short steps. Many studies have been reported on static mechanical properties of SLM components; however, dynamic properties of SLM components of different materials have not been thoroughly investigated. Only few papers have been published on the dynamic mechanical behavior, especially in the crack resistance of selective laser melted AlSi10Mg alloy. In the present study, the effect of loading rate, dynamic versus quasi static, on the fracture toughness of the as-built alloy (X and Z orientations) has been investigated. The experimental results revealed the inherently anisotropic behavior for loading rates where the Z orientation exhibited lower toughness compared to the x orientation. The dynamic loading by impact, resulted in a significant decrease of the toughness values up to about 50% compared to the quasi-static loading. This mechanical response was attributed to the increase in the yield stress which alters the state stress at the crack tip from the planestress to some extent of the mix-mode plane stress/strain.

A crystallographic study of the deformation mechanisms during small punch testing of 14wt%Cr oxide dispersion steel

Journal of Materials Science, Jun 8, 2022

Systematic study of the effect of Cr on the microstructure, phase content and hardness of the AlCrxFeCoNi alloys

Journal of Alloys and Compounds

Ion irradiation effect on B2 single phase AlFeCoNi alloy

Materials Characterization

Metallurgical and Materials Transactions B, 2011

The evolution of Ti-based nonmetallic inclusions in Maraging 250 steel, namely Ti(C x N 1-x) and ... more The evolution of Ti-based nonmetallic inclusions in Maraging 250 steel, namely Ti(C x N 1-x) and Ti 4 C 2 S 2 , was investigated experimentally. Their stability in austenite also was analyzed by a thermodynamic analysis of the Fe-Ni-TiC -N-S system. It was established that the total concentration of the inclusions decreases from 0.024 pct to 0.008 pct after treatment at 1453 K (1180°C) for 3 hours. The Ti 4 C 2 S 2 inclusions completely dissolve in austenite at 1523 K (1250°C) during 1 hour of treatment. The composition of the carbonitride inclusions is shifted toward higher TiN contents when they dissolve in austenite. Nitrogen-enriched titanium carbonitride inclusions are stable in austenite and their fraction may be reduced only by controlling nitrogen content in the steel. The experimental observations are in good agreement with the results of the thermodynamic analysis.

Early stages of interface reactions between AlN and Ti thin films

Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, 2002

ABSTRACT The early stages of interface reactions between AlN and Ti thin films were investigated ... more ABSTRACT The early stages of interface reactions between AlN and Ti thin films were investigated using x-ray diffractions, Auger electron spectroscopy, cross section transmission electron microscopy (XTEM), and high resolution XTEM. The AlN/Ti bilayers were deposited on a molybdenum substrate using reactive and nonreactive magnetron sputtering techniques. After deposition, the bilayers were heat treated for 1-10 h at 600 °C in a nitrogen atmosphere. Decomposition of the AlN layer took place at the AlN/Ti interface and its products, Al and N, reacted with Ti to produce a AlN/Al3Ti/Ti2N/Ti3Al/alpha-(Ti, Al)ss phase sequence. This phase sequence is not consistent with the Ti-Al-N phase diagram and is believed to be the outcome of the particular conditions that prevail in the thin film and correspond to a particular set of kinetic parameters. A model that explains the development of the phase sequence and predicts its evolution after prolonged heat treatments is put forward. The applicability of such a solid-state reaction technique for producing functionally graded coating for wear and corrosion resistance applications is discussed.

CORROSION, 2006

Hydrogen sensing using thermoelectric power (TEP) was performed on a nickel-copper alloy to asses... more Hydrogen sensing using thermoelectric power (TEP) was performed on a nickel-copper alloy to assess the hydrogen content resulting from cathodic protection. The measured TEP as a function of hydrogen content developed an anomaly at a specifi c hydrogen content, indicating a hydrogen-induced phase transformation in the alloy. The formation of Ni 2 H phase was found in a hydrogen-charged alloy (UNS N05500) using x-ray diffraction (XRD). The transmission electron microscopy (TEM) investigation of the hydrogen-charged alloy specimen revealed nano-sized Ni 2 H participates dispersed in the nickelcopper matrix. The measured TEP profi le correlated with an alloy hydride phase formation on a hydrogen-metal pressurecomposition-temperature (PCT) activity diagram. These results indicate that the TEP surface contact probe measurements can assist in the nondestructive evaluation (NDE) identifi cation of a microstructural change in hydrogen-charged nickel-copper alloys. With this TEP surface probe measurement technique, in situ determination of the susceptibility of an alloy to hydride formation is possible.

Microstructure characterization of ceramic composites formed by controlled melt oxidation of Al-Mg-Pd alloys

... The results of the present study indicate that the di-rected melt oxidation process can be co... more ... The results of the present study indicate that the di-rected melt oxidation process can be controlled by an appropriate choice of the elements added to the basic Al-Mg alloy. ... 12. K. C. VLACH, O. SALAS, H. NI, V. JAYARAM, C. G. LEVI and R. MEHRABIAN, J. Mater. Res. ...

Influence of alloying elements and the state of order on the formation of antiphase boundaries in B2 phases

Intermetallics

Metals

Quinary AlCoCrFeNi high entropy alloy (HEA) is one of the most studied alloys in the recent decad... more Quinary AlCoCrFeNi high entropy alloy (HEA) is one of the most studied alloys in the recent decade due to its outstanding properties. However, it is still far from becoming an applicable industrial alloy. To our understanding, in order to promote this, the role of elements, constituting the quinary alloy, needs to be defined. Knowing the role of each element, modification of the quinary alloy toward minimization of its disadvantages will be possible. In the current research, we shed some light on this subject, presenting a thorough investigation of the microstructure (carried out using scanning and transmission electron microscopy) and mechanical properties, performed by microhardness and fractography post small punch test (SPT), of five equiatomic quaternary alloys, constituting the quinary system, namely: CoCrFeNi, AlCoFeNi, AlCoCrNi, AlCoCrFe, and AlCrFeNi. CoCrFeNi (i.e., w/o Al) was found to be Face Centered Cubic (FCC) solid solution, exhibiting relatively low micro-hardness a...

Kinetics of the α-α′ phase separation in a 14%Cr oxide dispersion steel at intermediate temperatures

Materials Letters

Characterization of nano-sized particles in 14%Cr oxide dispersion strengthened (ODS) steel using classical and frontier microscopy methods

Materials Characterization

Abstract Oxide dispersion strengthened (ODS) steels exhibit superior mechanical properties and ir... more Abstract Oxide dispersion strengthened (ODS) steels exhibit superior mechanical properties and irradiation resistance due to nano-sized oxides, highly dispersed in the metallic matrix. The mechanical properties are affected by the structure, composition, size and density of the nano-sized oxides. Despite numerous reports on the characterization of these oxides, ambiguity regarding their composition, crystallographic structure and orientation relationship with the matrix remains. In the present study, characterization of the crystallographic structure of oxide particles existing in 14%Cr ODS steel was performed using classical and novel transmission electron microscopy (TEM) methods. 3D dispersion, density and composition of these oxides were evaluated by atom probe tomography (APT). Three populations of particles were detected: highly dispersed, 3–20 nm Fe(Cr,Ti,Y)O particles with spinel structure; 50–150 nm YTiO3 and large (100–200 nm) particles identified as cubic TiC. The spinel-type particles displayed Bain and Kurdjumov-Sachs orientation relationships (OR) with the ferritic matrix. Applying electron diffraction tomography, the YTiO3 structure was attributed to the GdFeO3 (distorted perovskite)-type and its lattice parameters were refined as a = 5.46 A, b = 7.66 A and c = 5.28 A. Orientation relationship of the YTiO3 particles and Fe matrix were determined as [110]Fe//[210]oxide and (110)Fe//(002)oxide.

Retardation of the σ phase formation in the AlCoCrFeNi multi-component alloy

Materials Characterization

The relation between aging temperature, microstructure evolution and hardening of Custom 465® stainless steel

Materials Characterization, 2017

International Journal of Refractory Metals and Hard Materials, 2010

The paper will present the state-of-art in the process, structure and properties of nanostructure... more The paper will present the state-of-art in the process, structure and properties of nanostructured multifunctional tribological coatings used in different industrial applications that require high hardness, toughness, wear resistance and thermal stability. The optimization of these coating systems by means of tailoring the structure (graded, superlattice and nanocomposite systems), composition optimization, and energetic ion bombardment from substrate bias voltage control to provide improved mechanical and tribological properties will be assessed for a range of coating systems, including nanocrystalline graded Cr 1Àx Al x N coatings, superlattice CrN/AlN coatings and nanocomposite Cr-B-N and TiC/a-C coatings. The results showed that the superlattice CrN/AlN coating exhibited a super hardness of 45 GPa when the bilayer period K was about 3.0 nm. Improved toughness and wear resistance have been achieved in the CrN/AlN multilayer and graded CrAlN coatings as compared to the homogeneous CrAlN coating. For the TiC/a-C coatings, increasing the substrate bias increased the hardness of TiC/a-C coatings up to 34 GPa (at À150 V) but also led to a decrease in the coating toughness and wear resistance. The TiC/a-C coating deposited at a À50 V bias voltage exhibited an optimized high hardness of 28 GPa, a low coefficient of friction of 0.19 and a wear rate of 2.37 Â 10 À7 mm 3 N À1 m À1. The Cr-B-N coating system consists of nanocrystalline CrB 2 embedded in an amorphous BN phase when the N content is low. With an increase in the N content, a decrease in the CrB 2 phase and an increase in the amorphous BN phase were identified. The resulting structure changes led to both decreases in the hardness and wear resistance of Cr-B-N coatings.

Pulsed Closed Field Unbalanced Magnetron Sputtering (P-CFUBMS) Deposited TiC/a:C Thin Films

Materials Science Forum, 2007

TiC/a:C nanocomposite thin film has proven to be a worthy material selection as a thin film for t... more TiC/a:C nanocomposite thin film has proven to be a worthy material selection as a thin film for tribological applications due to its low coefficient of friction, good wear resistance and high hardness. In the current study TiC/a:C thin films with carbon concentration near 55-62 at % were deposited via pulsed closed field unbalanced magnetron sputtering (P-CFUBMS) in pure argon atmosphere with different substrate bias voltages and onto 440C stainless steel substrate with different substrate roughness. It was found that the TiC/a:C film hardness and elastic modulus were increased from 18.5 GPa to 33.8 GPa by increasing the substrate bias from floating to -150 V. However higher substrate bias can also decrease the film tibological properties. The substrate roughness has a strong effect on TiC/a:C film wear behavior. When the Ra (Mean surface roughness values) is less than 110 nm, the COF values are in low range (0.18-0.28). Further increase the Ra value to above 300 nm will result in a higher COF (>0.33). Films deposited on higher surface roughness substrate need longer time to reach the sliding equilibrium state.

The origin of the effect of aging on the thermoelectric power of maraging C250 steel

Journal of Materials Science, 2015

ABSTRACT

Processing, Structure, and Properties of Nanostructured Multifunctional Tribological Coatings

Nanostructured, nanocomposite binary (TiC-a:C), ternary (Cr-Al-N), quaternary (Ti-B-C-N) and quin... more Nanostructured, nanocomposite binary (TiC-a:C), ternary (Cr-Al-N), quaternary (Ti-B-C-N) and quinternary (Ti-Si-B-C-N) multicomponent films have been deposited using unbalanced magnetron sputtering (UBMS) and closed field unbalanced magnetron sputtering (CFUBMS) from both elemental and composite targets. Approaches to control the film chemistry, volume fraction and size of the multicomponent species, and pulsed ion energy (ion flux) bombardment to tailor the structure and properties of the films for specific tribological applications, e.g., low friction coefficient and low wear rate, are emphasized. The synthesized films are characterized using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM), nanoindentation, and microtribometry. The relationships between processing parameters (pulsed ion energy and ion flux), thin film microstructure, mechanical and tribological properties are being investigated in terms of the nanocrystalline-nanocrystalline and nanocrystalline-amorphous composite thin film systems that are generated. In the Ti-Si-B-C-N films, nanocomposites of solid solutions, e.g., nanosized (Ti,C,N)B2 and Ti(C,N) crystallites are embedded in an amorphous TiSi2 and SiC matrix including some carbon, SiB4, BN, CN(x), TiO2 and B2O3 components. The Ti-Si-B-C-N coating with up to 150 W Si target power exhibited a hardness of about 35 GPa, a high H/E ratio of 0.095, and a low wear rate of from approximately 3 to approximately 10 x 10(-6) mm3/(Nm). In another aspect, using increased ion energy and ion flux, which are generated by pulsing the power of the target(s) in a closed field arrangement, to provide improved ion bombardment on tailoring the structure and properties of TiC-a:C and Cr-Al-N coatings are demonstrated. It was found that highly energetic species (up to hundreds eV) were found in the plasma by pulsing the power of the target(s) during magnetron sputtering. Applying higher pulse frequency and longer reverse time (lower duty cycle) will result in higher ion energy and ion flux in the plasma, which can be utilized to improve the film structure and properties. For example, optimum properties of the TiC-a:C coating were a hardness of 35 to 40 GPa and a COF of 0.2 to 0.22 for moderate maximum ion energies of 70 to 100 eV, and a super high hardness of 41 GPa and low wear rate of 3.41 x 10(-6) mm3N(-1) m(-1) was obtained for Cr-Al-N coatings deposited with a maximum ion energy of 122 eV. These conditions can be achieved by adjusting the pulsing parameters and target voltages. However, the pulsed ion energy together with the applied substrate bias are need to be carefully controlled in order to avoid excessive ion bombardment (e.g., the maximum ion energy is larger than 180 eV in the current study), which will responsible for an increase in point and line defects, and high residual stress in the crystalline structure.

Assessment of Hydrogen Cracking in N05500 Using TEP and XRD Analysis

Analele Universităţii "Dunărea de Jos" din Galaţi, Dec 28, 2018

In today's additive manufacturing sector, one of the most popular areas is selective laser meltin... more In today's additive manufacturing sector, one of the most popular areas is selective laser melting (SLM) due to its capability of producing geometrically complex metal parts directly from CAD model in a few short steps. Many studies have been reported on static mechanical properties of SLM components; however, dynamic properties of SLM components of different materials have not been thoroughly investigated. Only few papers have been published on the dynamic mechanical behavior, especially in the crack resistance of selective laser melted AlSi10Mg alloy. In the present study, the effect of loading rate, dynamic versus quasi static, on the fracture toughness of the as-built alloy (X and Z orientations) has been investigated. The experimental results revealed the inherently anisotropic behavior for loading rates where the Z orientation exhibited lower toughness compared to the x orientation. The dynamic loading by impact, resulted in a significant decrease of the toughness values up to about 50% compared to the quasi-static loading. This mechanical response was attributed to the increase in the yield stress which alters the state stress at the crack tip from the planestress to some extent of the mix-mode plane stress/strain.

A crystallographic study of the deformation mechanisms during small punch testing of 14wt%Cr oxide dispersion steel

Journal of Materials Science, Jun 8, 2022

Systematic study of the effect of Cr on the microstructure, phase content and hardness of the AlCrxFeCoNi alloys

Journal of Alloys and Compounds

Ion irradiation effect on B2 single phase AlFeCoNi alloy

Materials Characterization

Metallurgical and Materials Transactions B, 2011

The evolution of Ti-based nonmetallic inclusions in Maraging 250 steel, namely Ti(C x N 1-x) and ... more The evolution of Ti-based nonmetallic inclusions in Maraging 250 steel, namely Ti(C x N 1-x) and Ti 4 C 2 S 2 , was investigated experimentally. Their stability in austenite also was analyzed by a thermodynamic analysis of the Fe-Ni-TiC -N-S system. It was established that the total concentration of the inclusions decreases from 0.024 pct to 0.008 pct after treatment at 1453 K (1180°C) for 3 hours. The Ti 4 C 2 S 2 inclusions completely dissolve in austenite at 1523 K (1250°C) during 1 hour of treatment. The composition of the carbonitride inclusions is shifted toward higher TiN contents when they dissolve in austenite. Nitrogen-enriched titanium carbonitride inclusions are stable in austenite and their fraction may be reduced only by controlling nitrogen content in the steel. The experimental observations are in good agreement with the results of the thermodynamic analysis.

Early stages of interface reactions between AlN and Ti thin films

Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, 2002

ABSTRACT The early stages of interface reactions between AlN and Ti thin films were investigated ... more ABSTRACT The early stages of interface reactions between AlN and Ti thin films were investigated using x-ray diffractions, Auger electron spectroscopy, cross section transmission electron microscopy (XTEM), and high resolution XTEM. The AlN/Ti bilayers were deposited on a molybdenum substrate using reactive and nonreactive magnetron sputtering techniques. After deposition, the bilayers were heat treated for 1-10 h at 600 °C in a nitrogen atmosphere. Decomposition of the AlN layer took place at the AlN/Ti interface and its products, Al and N, reacted with Ti to produce a AlN/Al3Ti/Ti2N/Ti3Al/alpha-(Ti, Al)ss phase sequence. This phase sequence is not consistent with the Ti-Al-N phase diagram and is believed to be the outcome of the particular conditions that prevail in the thin film and correspond to a particular set of kinetic parameters. A model that explains the development of the phase sequence and predicts its evolution after prolonged heat treatments is put forward. The applicability of such a solid-state reaction technique for producing functionally graded coating for wear and corrosion resistance applications is discussed.

CORROSION, 2006

Hydrogen sensing using thermoelectric power (TEP) was performed on a nickel-copper alloy to asses... more Hydrogen sensing using thermoelectric power (TEP) was performed on a nickel-copper alloy to assess the hydrogen content resulting from cathodic protection. The measured TEP as a function of hydrogen content developed an anomaly at a specifi c hydrogen content, indicating a hydrogen-induced phase transformation in the alloy. The formation of Ni 2 H phase was found in a hydrogen-charged alloy (UNS N05500) using x-ray diffraction (XRD). The transmission electron microscopy (TEM) investigation of the hydrogen-charged alloy specimen revealed nano-sized Ni 2 H participates dispersed in the nickelcopper matrix. The measured TEP profi le correlated with an alloy hydride phase formation on a hydrogen-metal pressurecomposition-temperature (PCT) activity diagram. These results indicate that the TEP surface contact probe measurements can assist in the nondestructive evaluation (NDE) identifi cation of a microstructural change in hydrogen-charged nickel-copper alloys. With this TEP surface probe measurement technique, in situ determination of the susceptibility of an alloy to hydride formation is possible.

Microstructure characterization of ceramic composites formed by controlled melt oxidation of Al-Mg-Pd alloys

... The results of the present study indicate that the di-rected melt oxidation process can be co... more ... The results of the present study indicate that the di-rected melt oxidation process can be controlled by an appropriate choice of the elements added to the basic Al-Mg alloy. ... 12. K. C. VLACH, O. SALAS, H. NI, V. JAYARAM, C. G. LEVI and R. MEHRABIAN, J. Mater. Res. ...

Influence of alloying elements and the state of order on the formation of antiphase boundaries in B2 phases

Intermetallics

Metals

Quinary AlCoCrFeNi high entropy alloy (HEA) is one of the most studied alloys in the recent decad... more Quinary AlCoCrFeNi high entropy alloy (HEA) is one of the most studied alloys in the recent decade due to its outstanding properties. However, it is still far from becoming an applicable industrial alloy. To our understanding, in order to promote this, the role of elements, constituting the quinary alloy, needs to be defined. Knowing the role of each element, modification of the quinary alloy toward minimization of its disadvantages will be possible. In the current research, we shed some light on this subject, presenting a thorough investigation of the microstructure (carried out using scanning and transmission electron microscopy) and mechanical properties, performed by microhardness and fractography post small punch test (SPT), of five equiatomic quaternary alloys, constituting the quinary system, namely: CoCrFeNi, AlCoFeNi, AlCoCrNi, AlCoCrFe, and AlCrFeNi. CoCrFeNi (i.e., w/o Al) was found to be Face Centered Cubic (FCC) solid solution, exhibiting relatively low micro-hardness a...

Kinetics of the α-α′ phase separation in a 14%Cr oxide dispersion steel at intermediate temperatures

Materials Letters

Characterization of nano-sized particles in 14%Cr oxide dispersion strengthened (ODS) steel using classical and frontier microscopy methods

Materials Characterization

Abstract Oxide dispersion strengthened (ODS) steels exhibit superior mechanical properties and ir... more Abstract Oxide dispersion strengthened (ODS) steels exhibit superior mechanical properties and irradiation resistance due to nano-sized oxides, highly dispersed in the metallic matrix. The mechanical properties are affected by the structure, composition, size and density of the nano-sized oxides. Despite numerous reports on the characterization of these oxides, ambiguity regarding their composition, crystallographic structure and orientation relationship with the matrix remains. In the present study, characterization of the crystallographic structure of oxide particles existing in 14%Cr ODS steel was performed using classical and novel transmission electron microscopy (TEM) methods. 3D dispersion, density and composition of these oxides were evaluated by atom probe tomography (APT). Three populations of particles were detected: highly dispersed, 3–20 nm Fe(Cr,Ti,Y)O particles with spinel structure; 50–150 nm YTiO3 and large (100–200 nm) particles identified as cubic TiC. The spinel-type particles displayed Bain and Kurdjumov-Sachs orientation relationships (OR) with the ferritic matrix. Applying electron diffraction tomography, the YTiO3 structure was attributed to the GdFeO3 (distorted perovskite)-type and its lattice parameters were refined as a = 5.46 A, b = 7.66 A and c = 5.28 A. Orientation relationship of the YTiO3 particles and Fe matrix were determined as [110]Fe//[210]oxide and (110)Fe//(002)oxide.

Retardation of the σ phase formation in the AlCoCrFeNi multi-component alloy

Materials Characterization

The relation between aging temperature, microstructure evolution and hardening of Custom 465® stainless steel

Materials Characterization, 2017

International Journal of Refractory Metals and Hard Materials, 2010

The paper will present the state-of-art in the process, structure and properties of nanostructure... more The paper will present the state-of-art in the process, structure and properties of nanostructured multifunctional tribological coatings used in different industrial applications that require high hardness, toughness, wear resistance and thermal stability. The optimization of these coating systems by means of tailoring the structure (graded, superlattice and nanocomposite systems), composition optimization, and energetic ion bombardment from substrate bias voltage control to provide improved mechanical and tribological properties will be assessed for a range of coating systems, including nanocrystalline graded Cr 1Àx Al x N coatings, superlattice CrN/AlN coatings and nanocomposite Cr-B-N and TiC/a-C coatings. The results showed that the superlattice CrN/AlN coating exhibited a super hardness of 45 GPa when the bilayer period K was about 3.0 nm. Improved toughness and wear resistance have been achieved in the CrN/AlN multilayer and graded CrAlN coatings as compared to the homogeneous CrAlN coating. For the TiC/a-C coatings, increasing the substrate bias increased the hardness of TiC/a-C coatings up to 34 GPa (at À150 V) but also led to a decrease in the coating toughness and wear resistance. The TiC/a-C coating deposited at a À50 V bias voltage exhibited an optimized high hardness of 28 GPa, a low coefficient of friction of 0.19 and a wear rate of 2.37 Â 10 À7 mm 3 N À1 m À1. The Cr-B-N coating system consists of nanocrystalline CrB 2 embedded in an amorphous BN phase when the N content is low. With an increase in the N content, a decrease in the CrB 2 phase and an increase in the amorphous BN phase were identified. The resulting structure changes led to both decreases in the hardness and wear resistance of Cr-B-N coatings.

Pulsed Closed Field Unbalanced Magnetron Sputtering (P-CFUBMS) Deposited TiC/a:C Thin Films

Materials Science Forum, 2007

TiC/a:C nanocomposite thin film has proven to be a worthy material selection as a thin film for t... more TiC/a:C nanocomposite thin film has proven to be a worthy material selection as a thin film for tribological applications due to its low coefficient of friction, good wear resistance and high hardness. In the current study TiC/a:C thin films with carbon concentration near 55-62 at % were deposited via pulsed closed field unbalanced magnetron sputtering (P-CFUBMS) in pure argon atmosphere with different substrate bias voltages and onto 440C stainless steel substrate with different substrate roughness. It was found that the TiC/a:C film hardness and elastic modulus were increased from 18.5 GPa to 33.8 GPa by increasing the substrate bias from floating to -150 V. However higher substrate bias can also decrease the film tibological properties. The substrate roughness has a strong effect on TiC/a:C film wear behavior. When the Ra (Mean surface roughness values) is less than 110 nm, the COF values are in low range (0.18-0.28). Further increase the Ra value to above 300 nm will result in a higher COF (>0.33). Films deposited on higher surface roughness substrate need longer time to reach the sliding equilibrium state.

The origin of the effect of aging on the thermoelectric power of maraging C250 steel

Journal of Materials Science, 2015

ABSTRACT

Processing, Structure, and Properties of Nanostructured Multifunctional Tribological Coatings

Nanostructured, nanocomposite binary (TiC-a:C), ternary (Cr-Al-N), quaternary (Ti-B-C-N) and quin... more Nanostructured, nanocomposite binary (TiC-a:C), ternary (Cr-Al-N), quaternary (Ti-B-C-N) and quinternary (Ti-Si-B-C-N) multicomponent films have been deposited using unbalanced magnetron sputtering (UBMS) and closed field unbalanced magnetron sputtering (CFUBMS) from both elemental and composite targets. Approaches to control the film chemistry, volume fraction and size of the multicomponent species, and pulsed ion energy (ion flux) bombardment to tailor the structure and properties of the films for specific tribological applications, e.g., low friction coefficient and low wear rate, are emphasized. The synthesized films are characterized using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM), nanoindentation, and microtribometry. The relationships between processing parameters (pulsed ion energy and ion flux), thin film microstructure, mechanical and tribological properties are being investigated in terms of the nanocrystalline-nanocrystalline and nanocrystalline-amorphous composite thin film systems that are generated. In the Ti-Si-B-C-N films, nanocomposites of solid solutions, e.g., nanosized (Ti,C,N)B2 and Ti(C,N) crystallites are embedded in an amorphous TiSi2 and SiC matrix including some carbon, SiB4, BN, CN(x), TiO2 and B2O3 components. The Ti-Si-B-C-N coating with up to 150 W Si target power exhibited a hardness of about 35 GPa, a high H/E ratio of 0.095, and a low wear rate of from approximately 3 to approximately 10 x 10(-6) mm3/(Nm). In another aspect, using increased ion energy and ion flux, which are generated by pulsing the power of the target(s) in a closed field arrangement, to provide improved ion bombardment on tailoring the structure and properties of TiC-a:C and Cr-Al-N coatings are demonstrated. It was found that highly energetic species (up to hundreds eV) were found in the plasma by pulsing the power of the target(s) during magnetron sputtering. Applying higher pulse frequency and longer reverse time (lower duty cycle) will result in higher ion energy and ion flux in the plasma, which can be utilized to improve the film structure and properties. For example, optimum properties of the TiC-a:C coating were a hardness of 35 to 40 GPa and a COF of 0.2 to 0.22 for moderate maximum ion energies of 70 to 100 eV, and a super high hardness of 41 GPa and low wear rate of 3.41 x 10(-6) mm3N(-1) m(-1) was obtained for Cr-Al-N coatings deposited with a maximum ion energy of 122 eV. These conditions can be achieved by adjusting the pulsing parameters and target voltages. However, the pulsed ion energy together with the applied substrate bias are need to be carefully controlled in order to avoid excessive ion bombardment (e.g., the maximum ion energy is larger than 180 eV in the current study), which will responsible for an increase in point and line defects, and high residual stress in the crystalline structure.

Assessment of Hydrogen Cracking in N05500 Using TEP and XRD Analysis