Abstract The investment casting process was adopted to cast a low-pressure turbine rotor (LPTR) b... more Abstract The investment casting process was adopted to cast a low-pressure turbine rotor (LPTR) blisk. The casting was carried out in vacuum at 1525 °C by using BZL12Y superalloy. Ceramic shell moulds for the casting were prepared by two different fillers (mullite and zircon), two types of colloidal silica binders (polymer-free binder-A and polymer-containing binder-B) and cobalt aluminate solution. The shell specimens having binder B showed improved green strength and self-load sag resistance in comparison to their counterparts having binder-A. Samples prepared from the slurry compositions having binder-A showed higher residual fired strength than the samples prepared from slurry compositions having binder-B. Defect-free castings of LPTR blisks with fine equiaxed grains were obtained by using ceramic shell moulds containing binder-B and cobalt aluminate solution. The LPTR blisks cast from the ceramic shell moulds having binder-A showed hot tear defect along-with coarse grains. Irrespective of the filler, the LPTR blisk cast by using ceramic shell moulds and cobalt aluminate showed fine grains. The average surface roughness values of LPTR blisks cast from ceramic shell moulds, having binder-B and binder-A, were observed to be in the acceptable range even though castings with binder-A showed marginally lower surface roughness.
Abstract Zircon (ZrO2.SiO2) powder filler and colloidal silica binder were used to prepare the ce... more Abstract Zircon (ZrO2.SiO2) powder filler and colloidal silica binder were used to prepare the ceramic shell moulds for investment casting of shrouded low-pressure turbine blades (LPTB). Ceramic slurries were prepared by using two types of colloidal silica binders (polymer-free binder A and polymer-containing binder B). The samples prepared from binder B showed lesser self-load sag values than those developed from binder A. Ceramic shell moulds made from an optimized slurry composition (having binder A) yielded aeronautical grade casting of blades at 1500 °C with required dimensional accuracy and average surface roughness (Ra). The blades cast from shell moulds (having binder B) showed dimensional accuracy at 1500 °C as well as at 1525 °C. The Ra values of blades cast at 1500 °C and 1525 °C by using shell system with binder B were observed to be higher than those cast from shell system having binder A.
Abstract Zircon (ZrO2.SiO2) powder filler and colloidal silica binder were used to prepare the ce... more Abstract Zircon (ZrO2.SiO2) powder filler and colloidal silica binder were used to prepare the ceramic shell moulds for investment casting of shrouded low-pressure turbine blades (LPTB). Ceramic slurries were prepared by using two types of colloidal silica binders (polymer-free binder A and polymer-containing binder B). The samples prepared from binder B showed lesser self-load sag values than those developed from binder A. Ceramic shell moulds made from an optimized slurry composition (having binder A) yielded aeronautical grade casting of blades at 1500 °C with required dimensional accuracy and average surface roughness (Ra). The blades cast from shell moulds (having binder B) showed dimensional accuracy at 1500 °C as well as at 1525 °C. The Ra values of blades cast at 1500 °C and 1525 °C by using shell system with binder B were observed to be higher than those cast from shell system having binder A.
Abstract Nanostructured two-dimensional (2D) WS2 reinforced Al-4Cu alloy matrix composites were p... more Abstract Nanostructured two-dimensional (2D) WS2 reinforced Al-4Cu alloy matrix composites were prepared via spark plasma sintering (SPS) at 550 and 570 °C. The microstructure and interface characteristics of the composites were investigated. In situ formation of Al-W-Cu ternary phase at the grain boundaries of the Al-rich matrix phase was observed on sintering. High-resolution transmission electron microscopy (HRTEM) and scanning TEM (STEM) with quantitative mapping confirmed that the structure of ternary Al-W-Cu (Al12W0.6Cu0.4) belongs to bcc phase (space group: Im 3 (204), similar to that of binary bcc-Al12W phase. Such bcc intermetallic phase was absent in pure Al-matrix under identical sintering conditions. The ternary intermetallic phase along with the retained 2D-WS2 contributed to about 41% increase in the hardness of the alloy composite. Nanoindentation hardness and Young’s modulus of the Al-W-Cu ternary intermetallic were found to be around 4.6 GPa and 104 GPa, respectively. The formation mechanism of Al-W-Cu intermetallic phase from 2D-WS2 nanosheets and Al-4Cu matrix was elucidated with Calphad (Calculation of Phase Diagrams)-based Gibbs energy analysis.
Abstract This paper discusses an improvement in shell refractoriness and dimensional stability of... more Abstract This paper discusses an improvement in shell refractoriness and dimensional stability of columnar grained (CG) low pressure turbine blade castings made using Ni base superalloy by directional solidification process (DS). Two ceramic shell systems were adopted, namely shell system I and II. Shell moulds were prepared by using ceramic slurries containing zircon flour as a filler material and colloidal silica as a binder. As compared to shell system II (zircon filler with colloidal silica binder and fine alumina), shell system I (zircon filler with colloidal silica binder) showed lower refractoriness. Shell system II showed an increase in the flexural strength both in the green as well as in fired conditions. Shells made from shell system II showed about 13% higher green strength and 55% higher fired strength as compared to shell system I. Shell system II also exhibited superior self sag resistance up to 1625 °C. Moulds prepared from this shell system yielded aeronautical grade casting with high dimensional accuracy even at a metal pouring temperature of 1550 °C. Moulds from shell system I, on the other hand, underwent sagging even at metal pouring temperature of 1500 °C, leading to dimensionally unacceptable castings. The superior performance of shells prepared from shell system II can be ascribed to the presence of fine alumina in the shell.
Ceramic shell moulds for investment casting of shrouded low-pressure turbine (LPT) blades were pr... more Ceramic shell moulds for investment casting of shrouded low-pressure turbine (LPT) blades were prepared by using colloidal silica binder and partial substitution of the zircon filler with fine alumina. Among the two ceramic slurry systems designed, the first slurry system comprised of polymer-free colloidal silica binder, and the second slurry system comprised of polymer-containing colloidal silica binder. The samples prepared from the first slurry system showed higher fired residual strength and self-load sag values (lesser sag resistance). The casting of shrouded LPT blades was carried out at 1525 °C and 1550 °C using CM247LC superalloy. Ceramic shell moulds prepared from the second slurry system, containing 30 wt% of fine alumina filler, yielded aeronautical grade casting (at 1550 °C) of blades with required dimensional accuracy and average surface roughness. Microstructural analysis of the cut surfaces of self-load sag tested samples was carried out to understand the effect of f...
High-temperature oxidation behaviour of Mo-40Ti-30Si (at.%) alloy was investigated in the tempera... more High-temperature oxidation behaviour of Mo-40Ti-30Si (at.%) alloy was investigated in the temperature regime of 900-1300∘C in air. Isothermal weight change data recorded up to 100 h of exposure revealed parabolic weight gain kinetics at all the tested temperatures. The protective oxide scale composed with SiO2 (silica) and TiO2 (titania) forming a duplex oxide microstructure consisting of TiO2 particles embedded in the continuous SiO2 matrix. The oxide scale showed parabolic growth kinetics, and the activation energies for the scale growth were found to be 72.2 kJ/mol in 900-1200∘C and 324.9 kJ/mol in 1200-1300∘C. The kinetics of the protective scale growth on the alloy surface was mainly controlled by the growth of the silica film and the inward diffusion of oxygen through the duplex oxide layer.
Oxidation behavior of tungsten disulphide (WS2) nanosheet powder with an average thickness of abo... more Oxidation behavior of tungsten disulphide (WS2) nanosheet powder with an average thickness of about 10 nm was studied in the temperature range of 25-700°C. The samples were subjected to exposures...
Abstract Effect of Sm2O3 addition and two-step sintering of Ceria Stabilized Zirconia (CSZ) on mi... more Abstract Effect of Sm2O3 addition and two-step sintering of Ceria Stabilized Zirconia (CSZ) on microstructure and mechanical properties were investigated in the present work. Samaria doped CSZ (SmCSZ) nanopowders were prepared by co-precipitation synthesis from their respective nitrate salts. Synthesized powders were calcined at 1000 °C for 2 h and then compacted to ϕ10 mm pellets using a uniaxial hydraulic press. Single step & two-step sintering methods were used to sinter the compacted pellets. Powders and sintered pellets were characterized for phase and microstructure using X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) technique. Rietveld method was used for quantification of obtained phases. The hardness of the sintered samples was evaluated by Vicker's hardness tester, and toughness was estimated by indentation fracture toughness method. Samples sintered using two-step sintering method shown optimum hardness and toughness (up to 1288 HV10 and 5.37 MPa m1/2) values compared to conventionally sintered samples because of reduced grain size.
Abstract Effects of Nb2O5 addition to Ceria Stabilized Zirconia (CSZ) matrix within its solubilit... more Abstract Effects of Nb2O5 addition to Ceria Stabilized Zirconia (CSZ) matrix within its solubility limit on sinterability and mechanical properties (hardness and toughness) were investigated in this study. Sintered density and microstructure were correlated with hardness and fracture toughness. CSZ powders were prepared from nitrate salts of zirconia and ceria using co-precipitation method. Various amounts of Nb2O5 (0, 0.5, 1, 1.5 and 2 mol.%) powder were added to CSZ. The powders were compacted uniaxially and sintered in pressureless condition. Developed phases were identified using X-ray Diffraction (XRD) technique and quantified using Rietveld method. Microstructures were evaluated using Scanning Electron Microscope (SEM). Vickers hardness tester was used to find hardness and indentation fracture toughness of sintered samples. It was observed that addition of Nb2O5 improved sinterability with finer microstructure and near full density. 1 mol.% Nb2O5 doped CSZ (1NbCSZ) showed Vickers hardness value up to 1047 HV2 coupled with indentation fracture toughness value up to 6 M Pa m1/2 based on sintering schedule.
Abstract Four types of ceramic composites; ceria stabilized zirconia (CSZ), yttria stabilized zir... more Abstract Four types of ceramic composites; ceria stabilized zirconia (CSZ), yttria stabilized zirconia (YSZ), ceria stabilized zirconia toughened alumina (CSZ-TA) and yttria stabilized zirconia toughened alumina (YSZ-TA) were developed through powder metallurgy route using conventional pressure less resistance heating. Hydrothermal treatment was carried out to estimate the ageing stability of the developed materials. Fretting wear using ball on flat geometry were carried out before and after hydrothermal treatment to understand the effect of hydrothermal treatment on wear properties of developed materials. Variation of wear properties like wear depth, wear volume and coefficient of friction with duration of hydrothermal treatment was correlated with the microstructure and phase developed before and after hydrothermal treatment. It was found that presence of ceria decreases wear damage after hydrothermal treatment. For CSZ, wear volume decreased to 800×10 5 μm 3 from 1488×10 5 μm 3 while for YSZ it increased to 220×10 5 μm 3 from 28×10 5 μm 3 at 20 N load. Similar trend was found in CSZ-TA and YSZ-TA specimens also. It was understood that during hydrothermal treatment, a part of tetragonal phase of CSZ transforms to orthorhombic zirconia which in turn improves the wear properties.
Abstract Nano sized ceria stabilized zirconia (CSZ) powders were synthesized by co-precipitation ... more Abstract Nano sized ceria stabilized zirconia (CSZ) powders were synthesized by co-precipitation method and then sintered conventionally to near full density. Ageing stability of developed materials was predicted through in vitro hydrothermal treatment in the presence of simulated body fluid (SBF). Fretting wear test at different loads was carried out using balls on flat geometry at different intervals of hydrothermal treatment to observe the effects of surface ageing on wear properties. Wear volume, specific wear rate and wear depth were estimated through 3D profile scan of the worn out surface by a surface profiler and it was found that the developed material became more wear resistant with the increase in hydrothermal treatment duration. XRD analysis and hardness study suggest that formation of orthorhombic zirconia during hydrothermal treatment improves the surface hardness (from 946±86 HV20 to 964±39 HV20 after 100 h of hydrothermal treatment) which in turn enhances wear resistance. In vitro cytocompatibility of the developed materials was inferred through the formation of hydroxyapatite-like layer on the surface of the material when soaked in SBF at 37.5 °C. Cytocompatibility was further ensured by studding attachment of multilayered human osteoblast cells (MG63) on the surface during cell culture.
Abstract 15–25 wt% zirconia (stabilized with 14 mol% ceria) toughened alumina was synthesized by ... more Abstract 15–25 wt% zirconia (stabilized with 14 mol% ceria) toughened alumina was synthesized by co-precipitation technique. The synthesized powders were calcined at different temperatures, compacted and conventionally sintered following two steps sintering process. Uniformly distributed submicron sized grains with Vickers' hardness value up to 1730±6HV20 were achieved after conventional sintering. In order to assess the ageing behaviour, samples were hydrothermally treated (in vitro) at 134 °C under 0.2 MPa in presence of simulated body fluid. Rietveld refinement of the X-ray diffraction patterns was carried out to estimate the phase content after calcination, sintering and after different stages of hydrothermal treatment. No significant phase change (only ∼3%) was observed even after 100 h of hydrothermal treatment. Very few bulged grains (resulted from the tetragonal to monoclinic phase transformation) on the surface and slight decrease in hardness value were observed after hydrothermal treatment. Fretting wear in dry condition was carried out taking ball on flat geometry for 105 cycles at different loads before and after hydrothermal treatment. Wear volumes were directly estimated from the surface scanning of the wear scar using profilometer. Transition of wear and its related mechanisms at different loads along with the effect of ageing on wear were discussed.
Abstract The investment casting process was adopted to cast a low-pressure turbine rotor (LPTR) b... more Abstract The investment casting process was adopted to cast a low-pressure turbine rotor (LPTR) blisk. The casting was carried out in vacuum at 1525 °C by using BZL12Y superalloy. Ceramic shell moulds for the casting were prepared by two different fillers (mullite and zircon), two types of colloidal silica binders (polymer-free binder-A and polymer-containing binder-B) and cobalt aluminate solution. The shell specimens having binder B showed improved green strength and self-load sag resistance in comparison to their counterparts having binder-A. Samples prepared from the slurry compositions having binder-A showed higher residual fired strength than the samples prepared from slurry compositions having binder-B. Defect-free castings of LPTR blisks with fine equiaxed grains were obtained by using ceramic shell moulds containing binder-B and cobalt aluminate solution. The LPTR blisks cast from the ceramic shell moulds having binder-A showed hot tear defect along-with coarse grains. Irrespective of the filler, the LPTR blisk cast by using ceramic shell moulds and cobalt aluminate showed fine grains. The average surface roughness values of LPTR blisks cast from ceramic shell moulds, having binder-B and binder-A, were observed to be in the acceptable range even though castings with binder-A showed marginally lower surface roughness.
Abstract Zircon (ZrO2.SiO2) powder filler and colloidal silica binder were used to prepare the ce... more Abstract Zircon (ZrO2.SiO2) powder filler and colloidal silica binder were used to prepare the ceramic shell moulds for investment casting of shrouded low-pressure turbine blades (LPTB). Ceramic slurries were prepared by using two types of colloidal silica binders (polymer-free binder A and polymer-containing binder B). The samples prepared from binder B showed lesser self-load sag values than those developed from binder A. Ceramic shell moulds made from an optimized slurry composition (having binder A) yielded aeronautical grade casting of blades at 1500 °C with required dimensional accuracy and average surface roughness (Ra). The blades cast from shell moulds (having binder B) showed dimensional accuracy at 1500 °C as well as at 1525 °C. The Ra values of blades cast at 1500 °C and 1525 °C by using shell system with binder B were observed to be higher than those cast from shell system having binder A.
Abstract Zircon (ZrO2.SiO2) powder filler and colloidal silica binder were used to prepare the ce... more Abstract Zircon (ZrO2.SiO2) powder filler and colloidal silica binder were used to prepare the ceramic shell moulds for investment casting of shrouded low-pressure turbine blades (LPTB). Ceramic slurries were prepared by using two types of colloidal silica binders (polymer-free binder A and polymer-containing binder B). The samples prepared from binder B showed lesser self-load sag values than those developed from binder A. Ceramic shell moulds made from an optimized slurry composition (having binder A) yielded aeronautical grade casting of blades at 1500 °C with required dimensional accuracy and average surface roughness (Ra). The blades cast from shell moulds (having binder B) showed dimensional accuracy at 1500 °C as well as at 1525 °C. The Ra values of blades cast at 1500 °C and 1525 °C by using shell system with binder B were observed to be higher than those cast from shell system having binder A.
Abstract Nanostructured two-dimensional (2D) WS2 reinforced Al-4Cu alloy matrix composites were p... more Abstract Nanostructured two-dimensional (2D) WS2 reinforced Al-4Cu alloy matrix composites were prepared via spark plasma sintering (SPS) at 550 and 570 °C. The microstructure and interface characteristics of the composites were investigated. In situ formation of Al-W-Cu ternary phase at the grain boundaries of the Al-rich matrix phase was observed on sintering. High-resolution transmission electron microscopy (HRTEM) and scanning TEM (STEM) with quantitative mapping confirmed that the structure of ternary Al-W-Cu (Al12W0.6Cu0.4) belongs to bcc phase (space group: Im 3 (204), similar to that of binary bcc-Al12W phase. Such bcc intermetallic phase was absent in pure Al-matrix under identical sintering conditions. The ternary intermetallic phase along with the retained 2D-WS2 contributed to about 41% increase in the hardness of the alloy composite. Nanoindentation hardness and Young’s modulus of the Al-W-Cu ternary intermetallic were found to be around 4.6 GPa and 104 GPa, respectively. The formation mechanism of Al-W-Cu intermetallic phase from 2D-WS2 nanosheets and Al-4Cu matrix was elucidated with Calphad (Calculation of Phase Diagrams)-based Gibbs energy analysis.
Abstract This paper discusses an improvement in shell refractoriness and dimensional stability of... more Abstract This paper discusses an improvement in shell refractoriness and dimensional stability of columnar grained (CG) low pressure turbine blade castings made using Ni base superalloy by directional solidification process (DS). Two ceramic shell systems were adopted, namely shell system I and II. Shell moulds were prepared by using ceramic slurries containing zircon flour as a filler material and colloidal silica as a binder. As compared to shell system II (zircon filler with colloidal silica binder and fine alumina), shell system I (zircon filler with colloidal silica binder) showed lower refractoriness. Shell system II showed an increase in the flexural strength both in the green as well as in fired conditions. Shells made from shell system II showed about 13% higher green strength and 55% higher fired strength as compared to shell system I. Shell system II also exhibited superior self sag resistance up to 1625 °C. Moulds prepared from this shell system yielded aeronautical grade casting with high dimensional accuracy even at a metal pouring temperature of 1550 °C. Moulds from shell system I, on the other hand, underwent sagging even at metal pouring temperature of 1500 °C, leading to dimensionally unacceptable castings. The superior performance of shells prepared from shell system II can be ascribed to the presence of fine alumina in the shell.
Ceramic shell moulds for investment casting of shrouded low-pressure turbine (LPT) blades were pr... more Ceramic shell moulds for investment casting of shrouded low-pressure turbine (LPT) blades were prepared by using colloidal silica binder and partial substitution of the zircon filler with fine alumina. Among the two ceramic slurry systems designed, the first slurry system comprised of polymer-free colloidal silica binder, and the second slurry system comprised of polymer-containing colloidal silica binder. The samples prepared from the first slurry system showed higher fired residual strength and self-load sag values (lesser sag resistance). The casting of shrouded LPT blades was carried out at 1525 °C and 1550 °C using CM247LC superalloy. Ceramic shell moulds prepared from the second slurry system, containing 30 wt% of fine alumina filler, yielded aeronautical grade casting (at 1550 °C) of blades with required dimensional accuracy and average surface roughness. Microstructural analysis of the cut surfaces of self-load sag tested samples was carried out to understand the effect of f...
High-temperature oxidation behaviour of Mo-40Ti-30Si (at.%) alloy was investigated in the tempera... more High-temperature oxidation behaviour of Mo-40Ti-30Si (at.%) alloy was investigated in the temperature regime of 900-1300∘C in air. Isothermal weight change data recorded up to 100 h of exposure revealed parabolic weight gain kinetics at all the tested temperatures. The protective oxide scale composed with SiO2 (silica) and TiO2 (titania) forming a duplex oxide microstructure consisting of TiO2 particles embedded in the continuous SiO2 matrix. The oxide scale showed parabolic growth kinetics, and the activation energies for the scale growth were found to be 72.2 kJ/mol in 900-1200∘C and 324.9 kJ/mol in 1200-1300∘C. The kinetics of the protective scale growth on the alloy surface was mainly controlled by the growth of the silica film and the inward diffusion of oxygen through the duplex oxide layer.
Oxidation behavior of tungsten disulphide (WS2) nanosheet powder with an average thickness of abo... more Oxidation behavior of tungsten disulphide (WS2) nanosheet powder with an average thickness of about 10 nm was studied in the temperature range of 25-700°C. The samples were subjected to exposures...
Abstract Effect of Sm2O3 addition and two-step sintering of Ceria Stabilized Zirconia (CSZ) on mi... more Abstract Effect of Sm2O3 addition and two-step sintering of Ceria Stabilized Zirconia (CSZ) on microstructure and mechanical properties were investigated in the present work. Samaria doped CSZ (SmCSZ) nanopowders were prepared by co-precipitation synthesis from their respective nitrate salts. Synthesized powders were calcined at 1000 °C for 2 h and then compacted to ϕ10 mm pellets using a uniaxial hydraulic press. Single step & two-step sintering methods were used to sinter the compacted pellets. Powders and sintered pellets were characterized for phase and microstructure using X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) technique. Rietveld method was used for quantification of obtained phases. The hardness of the sintered samples was evaluated by Vicker's hardness tester, and toughness was estimated by indentation fracture toughness method. Samples sintered using two-step sintering method shown optimum hardness and toughness (up to 1288 HV10 and 5.37 MPa m1/2) values compared to conventionally sintered samples because of reduced grain size.
Abstract Effects of Nb2O5 addition to Ceria Stabilized Zirconia (CSZ) matrix within its solubilit... more Abstract Effects of Nb2O5 addition to Ceria Stabilized Zirconia (CSZ) matrix within its solubility limit on sinterability and mechanical properties (hardness and toughness) were investigated in this study. Sintered density and microstructure were correlated with hardness and fracture toughness. CSZ powders were prepared from nitrate salts of zirconia and ceria using co-precipitation method. Various amounts of Nb2O5 (0, 0.5, 1, 1.5 and 2 mol.%) powder were added to CSZ. The powders were compacted uniaxially and sintered in pressureless condition. Developed phases were identified using X-ray Diffraction (XRD) technique and quantified using Rietveld method. Microstructures were evaluated using Scanning Electron Microscope (SEM). Vickers hardness tester was used to find hardness and indentation fracture toughness of sintered samples. It was observed that addition of Nb2O5 improved sinterability with finer microstructure and near full density. 1 mol.% Nb2O5 doped CSZ (1NbCSZ) showed Vickers hardness value up to 1047 HV2 coupled with indentation fracture toughness value up to 6 M Pa m1/2 based on sintering schedule.
Abstract Four types of ceramic composites; ceria stabilized zirconia (CSZ), yttria stabilized zir... more Abstract Four types of ceramic composites; ceria stabilized zirconia (CSZ), yttria stabilized zirconia (YSZ), ceria stabilized zirconia toughened alumina (CSZ-TA) and yttria stabilized zirconia toughened alumina (YSZ-TA) were developed through powder metallurgy route using conventional pressure less resistance heating. Hydrothermal treatment was carried out to estimate the ageing stability of the developed materials. Fretting wear using ball on flat geometry were carried out before and after hydrothermal treatment to understand the effect of hydrothermal treatment on wear properties of developed materials. Variation of wear properties like wear depth, wear volume and coefficient of friction with duration of hydrothermal treatment was correlated with the microstructure and phase developed before and after hydrothermal treatment. It was found that presence of ceria decreases wear damage after hydrothermal treatment. For CSZ, wear volume decreased to 800×10 5 μm 3 from 1488×10 5 μm 3 while for YSZ it increased to 220×10 5 μm 3 from 28×10 5 μm 3 at 20 N load. Similar trend was found in CSZ-TA and YSZ-TA specimens also. It was understood that during hydrothermal treatment, a part of tetragonal phase of CSZ transforms to orthorhombic zirconia which in turn improves the wear properties.
Abstract Nano sized ceria stabilized zirconia (CSZ) powders were synthesized by co-precipitation ... more Abstract Nano sized ceria stabilized zirconia (CSZ) powders were synthesized by co-precipitation method and then sintered conventionally to near full density. Ageing stability of developed materials was predicted through in vitro hydrothermal treatment in the presence of simulated body fluid (SBF). Fretting wear test at different loads was carried out using balls on flat geometry at different intervals of hydrothermal treatment to observe the effects of surface ageing on wear properties. Wear volume, specific wear rate and wear depth were estimated through 3D profile scan of the worn out surface by a surface profiler and it was found that the developed material became more wear resistant with the increase in hydrothermal treatment duration. XRD analysis and hardness study suggest that formation of orthorhombic zirconia during hydrothermal treatment improves the surface hardness (from 946±86 HV20 to 964±39 HV20 after 100 h of hydrothermal treatment) which in turn enhances wear resistance. In vitro cytocompatibility of the developed materials was inferred through the formation of hydroxyapatite-like layer on the surface of the material when soaked in SBF at 37.5 °C. Cytocompatibility was further ensured by studding attachment of multilayered human osteoblast cells (MG63) on the surface during cell culture.
Abstract 15–25 wt% zirconia (stabilized with 14 mol% ceria) toughened alumina was synthesized by ... more Abstract 15–25 wt% zirconia (stabilized with 14 mol% ceria) toughened alumina was synthesized by co-precipitation technique. The synthesized powders were calcined at different temperatures, compacted and conventionally sintered following two steps sintering process. Uniformly distributed submicron sized grains with Vickers' hardness value up to 1730±6HV20 were achieved after conventional sintering. In order to assess the ageing behaviour, samples were hydrothermally treated (in vitro) at 134 °C under 0.2 MPa in presence of simulated body fluid. Rietveld refinement of the X-ray diffraction patterns was carried out to estimate the phase content after calcination, sintering and after different stages of hydrothermal treatment. No significant phase change (only ∼3%) was observed even after 100 h of hydrothermal treatment. Very few bulged grains (resulted from the tetragonal to monoclinic phase transformation) on the surface and slight decrease in hardness value were observed after hydrothermal treatment. Fretting wear in dry condition was carried out taking ball on flat geometry for 105 cycles at different loads before and after hydrothermal treatment. Wear volumes were directly estimated from the surface scanning of the wear scar using profilometer. Transition of wear and its related mechanisms at different loads along with the effect of ageing on wear were discussed.
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