Development of ultra high strength nano-Y2O3 dispersed ferritic steel by mechanical alloying and hot isostatic pressing (original) (raw)

Evaluation of Microstructure and Mechanical Properties of Nano-Y2O3-Dispersed Ferritic Alloy Synthesized by Mechanical Alloying and Consolidated by High-Pressure Sintering

Metallurgical and Materials Transactions, 2013

In this study, an attempt has been made to synthesize 1.0 wt % nano-Y 2 O 3 dispersed ferritic alloys with nominal compositions: 83.0Fe-13.5Cr-2.0Al-0.5Ti (alloy A), 79.0Fe-17.5Cr-2.0Al-0.5Ti (alloy B), 75.0Fe-21.5Cr-2.0Al-0.5Ti (alloy C), and 71.0Fe-25.5Cr-2.0Al-0.5Ti (alloy D) steels (all in wt %) by solid state mechanical alloying route and consolidation the milled powder by high pressure sintering at 873 K (600°C), 1073 K (800°C) and 1273 K (1000°C) using 8 GPa uniaxial pressure for 3 min. Subsequently, an extensive effort has been undertaken to characterize the microstructural and phase evolution by X-ray diffraction, scanning and transmission electron microscopy and energy dispersive spectroscopy. Mechanical properties including hardness, compressive strength, Young's modulus and fracture toughness were determined using micro/nano-indentation unit and universal testing machine. The present ferritic alloys record extraordinary levels of compressive strength (1150-2550 MPa), Young's modulus (200-240GPa), indentation fracture toughness (3.6 to 15.4 MPa√m) and hardness (13.5-18.5 GPa) and measure up to 1.5-2 times greater strength but with a lower density (~ 7.4 Mg/m 3) than other oxide dispersion strengthen ferritic steels (< 1200 MPa) or tungsten based alloys (< 2200 MPa). Besides superior mechanical strength, the novelty of these alloys lies in the unique microstructure comprising uniform distribution of either nanomertic (∼10 nm) oxide (Y 2 Ti 2 O 7 / Y 2 TiO 5 or unreacted Y 2 O 3) or intermetallic (Fe 11 TiY and Al 9.22 Cr 2.78 Y) particles ferritic matrix useful for grain boundary pinning and creep resistance.

Microstructure and mechanical properties of nano-Y2O3dispersed ferritic steel synthesized by mechanical alloying and consolidated by pulse plasma sintering

Philosophical Magazine, 2012

Ferritic steel with composition of 83.0Fe-13.5Cr-2.0Al-0.5Ti (alloy A), 79.0Fe-17.5Cr-2.0Al-0.5Ti (alloy B), 75.0Fe-21.5Cr-2.0Al-0.5Ti (alloy C) and 71.0Fe-25.5Cr-2.0Al-0.5Ti (alloy D) (all in wt %) each with 1.0 wt% nano-Y 2 O 3 dispersion were synthesized by mechanical alloying and consolidated by pulse plasma sintering at 600, 800 and 1000 °C using 75 MPa uniaxial pressure applied for 5 min and 70 kA pulse current at 3 Hz pulse frequency. X-ray diffraction, scanning and transmission electron microscopy and energy disperse spectroscopy techniques have been extensively used to characterize the microstructural and phase evolution of all the alloys at different stages of mechanochemical synthesis and consolidation. Mechanical properties in terms of hardness, compressive strength, yield strength and Young's modulus were determined using micro/nano-indentater and universal testing machine. The present ferritic alloys record very high levels of compressive strength (850-2850 MPa), yield strength (500-1556 MPa), Young's modulus (175-250 GPa) and nanoindentation hardness (9.5-15.5 GPa) and measure up to 1-1.5 times greater strength than other oxide dispersion strengthened ferritic steel (< 1200 MPa). These extraordinary levels of mechanical properties can be attributed to the typical microstructure comprising uniform dispersion of 10-20 nm Y 2 Ti 2 O 7 or Y 2 O 3 particles in high-alloy ferritic matrix.

Microstructure and mechanical properties of nano-Y2O3 dispersed ferritic alloys synthesized by mechanical alloying and consolidated by hydrostatic extrusion

Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2013

The present study reports synthesis of 1.0 wt % nano-Y 2 O 3 dispersed high strength ferritic alloys with nominal compositions of 83.0Fe-13.5Cr-2.0Al-0.5Ti (alloy A), 79.0Fe-17.5Cr-2.0Al-0.5Ti (alloy B) , 75.0Fe-21.5Cr-2.0Al-0.5Ti (alloy C) and 71.0Fe-25.5Cr-2.0Al-0.5Ti (alloy D) (all in wt %) by mechanical alloying using planetary ball mill followed by consolidation of alloyed powders by hydrostatic extrusion at 1000°C and 550 MPa pressure with a strain rate ~ 10 −1 s −1. The products of mechanical alloying and extrusion have been characterized by X-ray diffraction, scanning and transmission electron microscopy, energy dispersive spectroscopy and image analysis. Mechanical properties in terms of hardness, compressive strength, yield strength and Young's modulus have been determined using nano-indenter and universal testing machine. The present ferritic alloys record significantly high levels of compressive strength (850-2226 MPa) and yield strength (525-1505 MPa), Young's modulus (240-265 GPa) and hardness (14.7-17.8 GPa) with an impressive true strain (5.0-22.5 %). This extraordinary strength level measures up to 1.5 times greater strength, albeit with a lower density (~ 7.4 Mg/m 3) than that of (< 1200 MPa) standard oxide dispersion strengthened ferritic alloys. Furthermore, the extent of plastic strain before failure in the present routine surpasses all previous attempts of identical synthesis but different consolidation routes for the same set of ferritic alloys. In general strength is higher along transverse than longitudinal direction of extrusion. It is conclude that uniform dispersion of nanometric (20-30 nm) Y 2 O 3 (exsitu) or Y 2 Ti 2 O 7 (in-situ) in high volume fraction along boundaries and within the grains of high-Cr ferritic matrix is responsible for this unique combination of high strength and ductility in the present alloys developed by powder metallurgy route.

Microstructure and mechanical properties of nano-Y2O3 dispersed ferritic steel synthesized by mechanical alloying and consolidated by pulse plasma sintering

2012

Ferritic steel with compositions 83.0Fe-13.5Cr-2.0Al-0.5Ti (alloy A), 79.0Fe-17.5Cr-2.0Al-0.5Ti (alloy B), 75.0Fe-21.5Cr-2.0Al-0.5Ti (alloy C) and 71.0Fe-25.5Cr-2.0Al-0.5Ti (alloy D) (all in wt%) each with a 1.0wt% nano-Y2O3 dispersion were synthesized by mechanical alloying and consolidated by pulse plasma sintering at 600, 800 and 1000 degrees C using a 75-MPa uniaxial pressure applied for 5 min and a 70-kA pulse current at 3Hz pulse frequency. X-ray diffraction, scanning and transmission electron microscopy and energy disperse spectroscopy techniques have been used to characterize the microstructural and phase evolution of all the alloys at different stages of mechano-chemical synthesis and consolidation. Mechanical properties in terms of hardness, compressive strength, yield strength and Young's modulus were determined using a micro/nano-indenter and universal testing machine. All ferritic alloys recorded very high levels of compressive strength (850-2850 MPa), yield strengt...

The Effect of Annealing to the Hardness of High Y2O3-Oxide Dispersion Strengthened (ODS) Ferritic Steels

Sains Malaysiana

The purpose of this study was to investigate the effect of annealing to the hardness of high Y 2 O 3-oxide dispersion strengthened (ODS) ferritic steels. The samples were prepared by mechanical alloying method followed by Cold Isostatic Pressing (CIP). After compaction process, the samples were sintered at 1100°C for 1 h in a tube furnace. The crystal structure and morphology of samples were analyzed by X-ray Diffraction (XRD) measurement and characterized by using field emission scanning electron microscope (FESEM), respectively. The hardness of samples was measured by using a micro-Vickers hardness tester with a load of 200 gf at annealing temperature of 600°C, 800°C and 1000°C, respectively. The Vickers hardness value (HV0,2) versus annealing temperature graph showed that the hardness of all samples started to decrease at temperature of 600°C due to grain growth. The hardness value of all samples (1Y and 5Y) identified at this annealing temperature is 855 HV0,2 and 808 HV0, 2, respectively.

Microstructural evolution and some mechanical properties of nanosized yttrium oxide dispersion strengthened 13Cr steelReport submitted to the 5th International Workshop on Advanced Materials Science and Nanotechnology IWAMSN, Hanoi, 9–12 November 2010

Advances in Natural Sciences: Nanoscience and Nanotechnology, 2010

Oxide dispersion strengthened (ODS) steels, manufactured by a mechanical alloying method, during the past few years, appear to be promising candidates for structural applications in nuclear power plants. The purpose of this work is to elaborate the manufacturing processes of ODS 13Cr steel with the addition of 1.0 wt% yttrium oxide through the powder metallurgy route using the high energy ball mill. Microstructural analysis by scanning electron microscopy (SEM), x-ray diffraction (XRD) and hardness testing have been used to optimize the technological parameters of milling, hot isostatic pressing and heat-treatment processes. The steel hardness increases with decreasing particle size of 13Cr ODS steel. The best hardness was obtained from more than 70 h of milling in the two tanks planetary ball mill or 30 h of milling in the one tank planetary ball mill and hot isostatic pressing at 1150 • C . The particle size of the steel is less than 100 nm, and the density and hardness are about 7.3 g cm −3 and 490 HB, respectively.

Microstructural characterization of oxide dispersion strengthened ferritic steel powder

Journal of Nuclear Materials, 2013

Oxide dispersion strengthened ferritic steel powder was prepared by mechanical alloying of pre-alloyed ferritic steel powder together with nano Y 2 O 3 in a dual drive planetary ball mill. A detailed investigation was carried out using X-ray diffraction, field emission electron microscopy and transmission electron microscopy. Microstructural parameters such as, crystallite size, lattice strain, deformation stress and dislocation character were evaluated using different Williamson-Hall models; uniform deformation model, uniform stress deformation model and modified Williamson-Hall model and the results obtained were compared and discussed. Uniform stress deformation model and modified Williamson-Hall model were observed to give better estimation of crystallite size as they consider strain anisotropy. With mil ling, dislocation character was observed to be changing, from near edge to mixed type. Lattice parameters of the milled powders were also estimated. Uniform milling with convoluted particle shape and homogeneous distribution of Y 2 O 3 throughout the matrix was observed by using electron microscopy.

Studies on wear behavior of nano-Y2O3 dispersed ferritic steel developed by mechanical alloying and hot isostatic pressing

Wear, 2010

Resistance to wear is an important factor in design and selection of structural components in motion and in contact with a mating surface. The present work deals with studies on fretting wear behavior of mechanically alloyed 1.0 wt.% nano-Y 2 O 3 dispersed 71.0Fe-25.5Cr-2.0Al-0.5Ti (wt.%) ferritic steel consolidated by hot isostatic pressing at 600, 800 and 1000 • C under 1.2 GPa uniaxial pressure applied for 1 h. The wear experiments were carried out in gross slip fretting regime against 6 mm diameter tungsten carbide ball at ambient temperature. The highest resistance to fretting wear has been observed in the alloy sintered at 1000 • C. The fretting involves localized plastic deformation and oxidation as evidenced by post wear surface profile and micro-compositional analysis, respectively.

Optimization of milling parameters, processing and characterization of nano-crystalline oxide dispersion strengthened ferritic steel

Powder Technology, 2014

Ferritic steel powder was mechanically milled in a dual drive planetary ball mill, under different milling conditions to optimize the milling parameters. The resulted powder was characterized, using particle size analyzer, X-rays and electron microscope. X-ray peak broadenings were investigated to estimate crystallite size, lattice strain and deformation stress. Better Pearson's coefficient was observed for uniform stress deformation model (USDM) (0.988) in comparison to uniform deformation model (UDM) (0.64) which shows better estimation of lattice parameter. An increase in fineness was observed with an increase in ball to powder ratio as well as for an increase in rotational speed. At the optimized condition, ferritic steel powder, together with Y 2 O 3 , was milled in the dual drive mill to produce oxide dispersion strengthened ferritic steel powder, suitable to be used in nuclear applications. Convoluted morphology, desired for better alloying, was confirmed using an electron microscope. A significant increase in per unit surface area was noticed due to milling using BET surface area analysis. Negligible contamination was observed due to milling atmosphere and mill container. The steel powder produced, was sintered using spark plasma sintering and its density and hardness were measured. High hardness and lower crystallite size were recorded using spark plasma sintering. Addition of Y 2 O 3 shows decreases in the thermal expansion coefficient. Effect of added titanium was studied and an adverse effect on oxide dispersion strengthened steel was noticed.

Microstructural evolution and some mechanical properties of nanosized yttrium oxide dispersion strengthened 13Cr steel

Advances in Natural …, 2010

Oxide dispersion strengthened (ODS) steels, manufactured by a mechanical alloying method, during the past few years, appear to be promising candidates for structural applications in nuclear power plants. The purpose of this work is to elaborate the manufacturing processes of ODS 13Cr steel with the addition of 1.0 wt% yttrium oxide through the powder metallurgy route using the high energy ball mill. Microstructural analysis by scanning electron microscopy (SEM), x-ray diffraction (XRD) and hardness testing have been used to optimize the technological parameters of milling, hot isostatic pressing and heat-treatment processes. The steel hardness increases with decreasing particle size of 13Cr ODS steel. The best hardness was obtained from more than 70 h of milling in the two tanks planetary ball mill or 30 h of milling in the one tank planetary ball mill and hot isostatic pressing at 1150 • C. The particle size of the steel is less than 100 nm, and the density and hardness are about 7.3 g cm −3 and 490 HB, respectively.