G. Jhala - Academia.edu (original) (raw)

Papers by G. Jhala

Surface and Coatings Technology, 2013

Plasma nitriding is widely used for the improvement of the mechanical/tribological properties of ... more Plasma nitriding is widely used for the improvement of the mechanical/tribological properties of various steel components in many applications such as automobile parts, turbine parts, textile machinery parts, etc. However, plasma nitriding on components with welding joints have not been intensively studied so far. In this study, we attempted to study the welded region of AISI 304 stainless steel after carrying out the plasma nitriding process. The plasma nitriding of stainless steel welded joints has been done with a H 2 :N 2 (4:1) gas mixture at 570 and 450°C for different time durations. The parent and the welded regions were characterized using a microhardness tester, a scanning electron microscope (SEM) and an X-ray diffractometer (XRD) for surface hardness, case depth and phase formation respectively. The results show that the nitrided layer formed on the welded region consists of Fe 4 N and Fe 3 N, CrN and γ phases. Also, welded joints using the multiple pass technique gave better nitriding properties compared with that of the single pass technique. There is an improvement in the hardness by 3 times which could be correlated with structural changes and process parameters.

Physical Review B, 2005

Precipitation hardening of copper alloys results in improved elastic properties but is accompanie... more Precipitation hardening of copper alloys results in improved elastic properties but is accompanied by reduction in electrical conductivity. We study the electronic structure, microstructure, and crystal structure of precipitation-hardened Cu:Be:Co (98:1.8:0.2 weight %) alloy to look for coupled changes accompanying the precipitation hardening. X-ray diffraction is used to study the strain in the Cu matrix upon Guinier-Preston zone formation and

The paper presents the results of investigations of the structure and corrosion resistance of AIS... more The paper presents the results of investigations of the structure and corrosion resistance of AISI 4340 steel after plasma nitriding with 10 kHz and 30 kHz pulse frequencies. Properties of the nitrided layer were analysed by using Scanning Electron Microscope (SEM), X-Ray Diffractometer (XRD) and micro-Vickers hardness tester. Corrosion rates were monitored through polarisation resistance technique using 3% NaCl solution. In our present work, it was found that plasma nitriding with 30 kHz frequency gave better corrosion resistance and higher surface hardness than 10 kHz on AISI 4340 steel.

Grade 2205 duplex stainless steel is a type of stainless steel possessing a nearly equal amount o... more Grade 2205 duplex stainless steel is a type of stainless steel possessing a nearly equal amount of the ferrite (α-Fe) and austenite (γ-Fe) phases as a matrix. Since this steel has a relatively low hardness of 256 HV0.1, an attempt has been made to improve its hardness and wear properties without compromising the corrosion resistance by plasma nitriding and nitrocarburising process. Plasma nitriding and plasma nitrocarburising process was performed with 80% nitrogen and 20% hydrogen gas and 78% nitrogen, 20% hydrogen and 2% acetylene gas respectively at 350, 400, 450 and 500 o C for 4 hours. The temperature played an important role in the distribution of nitrogen and carbon in the original austenite and ferrite phases present in the bulk material. As a result there was an improvement in microhardness and corrosion properties after these treatments. It was observed that plasma nitrocarburising process performed better than plasma nitriding process in improving the corrosion properties...

Plasma nitriding has potential as an industrial process to improve the wear, fatigue and corrosio... more Plasma nitriding has potential as an industrial process to improve the wear, fatigue and corrosion resistance of steels. It is well known that the corrosion properties of stainless steel deteriorate when treated with temperatures above 450°C. This is because the chromium-alloying element, which is responsible for protection against corrosion, gets converted to chromium nitrides at these temperatures. Whereas low alloy steels and high alloy steels exhibit better corrosion resistance. This is due to the presence of iron nitrides and few chromium nitride phases. In this study an attempt is made to study the effect of alloying elements on the corrosion properties of EN 8 (AISI 1045), En 24 (AISI 4340), AISI H13 and AISI 304 steels during plasma nitriding.

Grade 2205 duplex stainless steel is a type of stainless steel possessing a nearly equal amount o... more Grade 2205 duplex stainless steel is a type of stainless steel possessing a nearly equal amount of the ferrite (α-Fe) and austenite (γ-Fe) phases as a matrix. Since this steel has a relatively low hardness of 256 HV0.1, an attempt has been made to improve its hardness and wear properties without compromising the corrosion resistance by plasma nitriding and nitrocarburising process. Plasma nitriding and plasma nitrocarburising process was performed with 80% nitrogen and 20% hydrogen gas and 78% nitrogen, 20% hydrogen and 2% acetylene gas respectively at 350, 400, 450 and 500 o C for 4 hours. The temperature played an important role in the distribution of nitrogen and carbon in the original austenite and ferrite phases present in the bulk material. As a result there was an improvement in microhardness and corrosion properties after these treatments. It was observed that plasma nitrocarburising process performed better than plasma nitriding process in improving the corrosion properties...

Surface Engineering, 2012

Surface and Coatings Technology, 2013

Plasma nitriding is widely used for the improvement of the mechanical/tribological properties of ... more Plasma nitriding is widely used for the improvement of the mechanical/tribological properties of various steel components in many applications such as automobile parts, turbine parts, textile machinery parts, etc. However, plasma nitriding on components with welding joints have not been intensively studied so far. In this study, we attempted to study the welded region of AISI 304 stainless steel after carrying out the plasma nitriding process. The plasma nitriding of stainless steel welded joints has been done with a H 2 :N 2 (4:1) gas mixture at 570 and 450°C for different time durations. The parent and the welded regions were characterized using a microhardness tester, a scanning electron microscope (SEM) and an X-ray diffractometer (XRD) for surface hardness, case depth and phase formation respectively. The results show that the nitrided layer formed on the welded region consists of Fe 4 N and Fe 3 N, CrN and γ phases. Also, welded joints using the multiple pass technique gave better nitriding properties compared with that of the single pass technique. There is an improvement in the hardness by 3 times which could be correlated with structural changes and process parameters.

Physical Review B, 2005

Precipitation hardening of copper alloys results in improved elastic properties but is accompanie... more Precipitation hardening of copper alloys results in improved elastic properties but is accompanied by reduction in electrical conductivity. We study the electronic structure, microstructure, and crystal structure of precipitation-hardened Cu:Be:Co (98:1.8:0.2 weight %) alloy to look for coupled changes accompanying the precipitation hardening. X-ray diffraction is used to study the strain in the Cu matrix upon Guinier-Preston zone formation and

Diabetes, 2012

Prevention of autoimmunity requires the elimination of selfreactive T cells during their developm... more Prevention of autoimmunity requires the elimination of selfreactive T cells during their development in the thymus and maturation in the periphery. Transgenic NOD mice that overexpress islet-specific glucose 6 phosphatase catalytic subunitrelated protein (IGRP) in antigen-presenting cells (NOD-IGRP mice) have no IGRP-specific T cells. To study the relative contribution of central and peripheral tolerance mechanisms to deletion of antigen-specific T cells, we crossed NOD-IGRP mice to highly diabetogenic IGRP 206-214 T-cell receptor transgenic mice (NOD8.3 mice) and studied the frequency and function of IGRP-specific T cells in the thymus and periphery. Peripheral tolerance was extremely efficient and completely protected NOD-IGRP/NOD8.3 mice from diabetes. Peripheral tolerance was characterized by activation of T cells in peripheral lymphoid tissue where IGRP was expressed followed by activation-induced cell death. Thymectomy showed that thymic output of IGRP-specific transgenic T cells compensated for peripheral deletion to maintain peripheral T-cell numbers. Central tolerance was undetectable until 10 weeks and complete by 15 weeks. These in vivo data indicate that peripheral tolerance alone can protect NOD8.3 mice from autoimmune diabetes and that profound changes in T-cell repertoire can follow subtle changes in thymic antigen presentation. Diabetes 61:425-435, 2012 B y exposing developing thymocytes to self-antigens, the thymus purges the majority of autoreactive T cells by a process called negative selection. Experiments in animal models have demonstrated that stromal medullary thymic epithelial cells (ECs) and bone marrow-derived thymic dendritic cells (DCs) play an important role by expressing self-antigens to mediate thymocyte negative selection (1). Many, but not all, tissue-specific antigens that are expressed in medullary thymic ECs are controlled by the autoimmune regulator (AIRE) transcription factor (2-5). Thymic DCs have been shown to broaden the spectrum of self-antigens presented to developing T cells either by expressing self-antigens or presenting self-antigens after capturing them from medullary ECs (6).

Plasma nitriding has potential as an industrial process to improve the wear, fatigue and corrosio... more Plasma nitriding has potential as an industrial process to improve the wear, fatigue and corrosion resistance of steels. It is well known that the corrosion properties of stainless steel deteriorate when treated with temperatures above 450 0 C. This is because the chromium-alloying element, which is responsible for protection against corrosion, gets converted to chromium nitrides at these temperatures. Whereas low alloy steels and high alloy steels exhibit better corrosion resistance. This is due to the presence of iron nitrides and few chromium nitride phases. In this study an attempt is made to study the effect of alloying elements on the corrosion properties of EN 8 (AISI 1045), En 24 (AISI 4340), AISI H13 and AISI 304 steels during plasma nitriding.

Surface and Coatings Technology, 2013

Plasma nitriding is widely used for the improvement of the mechanical/tribological properties of ... more Plasma nitriding is widely used for the improvement of the mechanical/tribological properties of various steel components in many applications such as automobile parts, turbine parts, textile machinery parts, etc. However, plasma nitriding on components with welding joints have not been intensively studied so far. In this study, we attempted to study the welded region of AISI 304 stainless steel after carrying out the plasma nitriding process. The plasma nitriding of stainless steel welded joints has been done with a H 2 :N 2 (4:1) gas mixture at 570 and 450°C for different time durations. The parent and the welded regions were characterized using a microhardness tester, a scanning electron microscope (SEM) and an X-ray diffractometer (XRD) for surface hardness, case depth and phase formation respectively. The results show that the nitrided layer formed on the welded region consists of Fe 4 N and Fe 3 N, CrN and γ phases. Also, welded joints using the multiple pass technique gave better nitriding properties compared with that of the single pass technique. There is an improvement in the hardness by 3 times which could be correlated with structural changes and process parameters.

Physical Review B, 2005

Precipitation hardening of copper alloys results in improved elastic properties but is accompanie... more Precipitation hardening of copper alloys results in improved elastic properties but is accompanied by reduction in electrical conductivity. We study the electronic structure, microstructure, and crystal structure of precipitation-hardened Cu:Be:Co (98:1.8:0.2 weight %) alloy to look for coupled changes accompanying the precipitation hardening. X-ray diffraction is used to study the strain in the Cu matrix upon Guinier-Preston zone formation and

The paper presents the results of investigations of the structure and corrosion resistance of AIS... more The paper presents the results of investigations of the structure and corrosion resistance of AISI 4340 steel after plasma nitriding with 10 kHz and 30 kHz pulse frequencies. Properties of the nitrided layer were analysed by using Scanning Electron Microscope (SEM), X-Ray Diffractometer (XRD) and micro-Vickers hardness tester. Corrosion rates were monitored through polarisation resistance technique using 3% NaCl solution. In our present work, it was found that plasma nitriding with 30 kHz frequency gave better corrosion resistance and higher surface hardness than 10 kHz on AISI 4340 steel.

Grade 2205 duplex stainless steel is a type of stainless steel possessing a nearly equal amount o... more Grade 2205 duplex stainless steel is a type of stainless steel possessing a nearly equal amount of the ferrite (α-Fe) and austenite (γ-Fe) phases as a matrix. Since this steel has a relatively low hardness of 256 HV0.1, an attempt has been made to improve its hardness and wear properties without compromising the corrosion resistance by plasma nitriding and nitrocarburising process. Plasma nitriding and plasma nitrocarburising process was performed with 80% nitrogen and 20% hydrogen gas and 78% nitrogen, 20% hydrogen and 2% acetylene gas respectively at 350, 400, 450 and 500 o C for 4 hours. The temperature played an important role in the distribution of nitrogen and carbon in the original austenite and ferrite phases present in the bulk material. As a result there was an improvement in microhardness and corrosion properties after these treatments. It was observed that plasma nitrocarburising process performed better than plasma nitriding process in improving the corrosion properties...

Plasma nitriding has potential as an industrial process to improve the wear, fatigue and corrosio... more Plasma nitriding has potential as an industrial process to improve the wear, fatigue and corrosion resistance of steels. It is well known that the corrosion properties of stainless steel deteriorate when treated with temperatures above 450°C. This is because the chromium-alloying element, which is responsible for protection against corrosion, gets converted to chromium nitrides at these temperatures. Whereas low alloy steels and high alloy steels exhibit better corrosion resistance. This is due to the presence of iron nitrides and few chromium nitride phases. In this study an attempt is made to study the effect of alloying elements on the corrosion properties of EN 8 (AISI 1045), En 24 (AISI 4340), AISI H13 and AISI 304 steels during plasma nitriding.

Grade 2205 duplex stainless steel is a type of stainless steel possessing a nearly equal amount o... more Grade 2205 duplex stainless steel is a type of stainless steel possessing a nearly equal amount of the ferrite (α-Fe) and austenite (γ-Fe) phases as a matrix. Since this steel has a relatively low hardness of 256 HV0.1, an attempt has been made to improve its hardness and wear properties without compromising the corrosion resistance by plasma nitriding and nitrocarburising process. Plasma nitriding and plasma nitrocarburising process was performed with 80% nitrogen and 20% hydrogen gas and 78% nitrogen, 20% hydrogen and 2% acetylene gas respectively at 350, 400, 450 and 500 o C for 4 hours. The temperature played an important role in the distribution of nitrogen and carbon in the original austenite and ferrite phases present in the bulk material. As a result there was an improvement in microhardness and corrosion properties after these treatments. It was observed that plasma nitrocarburising process performed better than plasma nitriding process in improving the corrosion properties...

Surface Engineering, 2012

Surface and Coatings Technology, 2013

Plasma nitriding is widely used for the improvement of the mechanical/tribological properties of ... more Plasma nitriding is widely used for the improvement of the mechanical/tribological properties of various steel components in many applications such as automobile parts, turbine parts, textile machinery parts, etc. However, plasma nitriding on components with welding joints have not been intensively studied so far. In this study, we attempted to study the welded region of AISI 304 stainless steel after carrying out the plasma nitriding process. The plasma nitriding of stainless steel welded joints has been done with a H 2 :N 2 (4:1) gas mixture at 570 and 450°C for different time durations. The parent and the welded regions were characterized using a microhardness tester, a scanning electron microscope (SEM) and an X-ray diffractometer (XRD) for surface hardness, case depth and phase formation respectively. The results show that the nitrided layer formed on the welded region consists of Fe 4 N and Fe 3 N, CrN and γ phases. Also, welded joints using the multiple pass technique gave better nitriding properties compared with that of the single pass technique. There is an improvement in the hardness by 3 times which could be correlated with structural changes and process parameters.

Physical Review B, 2005

Precipitation hardening of copper alloys results in improved elastic properties but is accompanie... more Precipitation hardening of copper alloys results in improved elastic properties but is accompanied by reduction in electrical conductivity. We study the electronic structure, microstructure, and crystal structure of precipitation-hardened Cu:Be:Co (98:1.8:0.2 weight %) alloy to look for coupled changes accompanying the precipitation hardening. X-ray diffraction is used to study the strain in the Cu matrix upon Guinier-Preston zone formation and

Diabetes, 2012

Prevention of autoimmunity requires the elimination of selfreactive T cells during their developm... more Prevention of autoimmunity requires the elimination of selfreactive T cells during their development in the thymus and maturation in the periphery. Transgenic NOD mice that overexpress islet-specific glucose 6 phosphatase catalytic subunitrelated protein (IGRP) in antigen-presenting cells (NOD-IGRP mice) have no IGRP-specific T cells. To study the relative contribution of central and peripheral tolerance mechanisms to deletion of antigen-specific T cells, we crossed NOD-IGRP mice to highly diabetogenic IGRP 206-214 T-cell receptor transgenic mice (NOD8.3 mice) and studied the frequency and function of IGRP-specific T cells in the thymus and periphery. Peripheral tolerance was extremely efficient and completely protected NOD-IGRP/NOD8.3 mice from diabetes. Peripheral tolerance was characterized by activation of T cells in peripheral lymphoid tissue where IGRP was expressed followed by activation-induced cell death. Thymectomy showed that thymic output of IGRP-specific transgenic T cells compensated for peripheral deletion to maintain peripheral T-cell numbers. Central tolerance was undetectable until 10 weeks and complete by 15 weeks. These in vivo data indicate that peripheral tolerance alone can protect NOD8.3 mice from autoimmune diabetes and that profound changes in T-cell repertoire can follow subtle changes in thymic antigen presentation. Diabetes 61:425-435, 2012 B y exposing developing thymocytes to self-antigens, the thymus purges the majority of autoreactive T cells by a process called negative selection. Experiments in animal models have demonstrated that stromal medullary thymic epithelial cells (ECs) and bone marrow-derived thymic dendritic cells (DCs) play an important role by expressing self-antigens to mediate thymocyte negative selection (1). Many, but not all, tissue-specific antigens that are expressed in medullary thymic ECs are controlled by the autoimmune regulator (AIRE) transcription factor (2-5). Thymic DCs have been shown to broaden the spectrum of self-antigens presented to developing T cells either by expressing self-antigens or presenting self-antigens after capturing them from medullary ECs (6).

Plasma nitriding has potential as an industrial process to improve the wear, fatigue and corrosio... more Plasma nitriding has potential as an industrial process to improve the wear, fatigue and corrosion resistance of steels. It is well known that the corrosion properties of stainless steel deteriorate when treated with temperatures above 450 0 C. This is because the chromium-alloying element, which is responsible for protection against corrosion, gets converted to chromium nitrides at these temperatures. Whereas low alloy steels and high alloy steels exhibit better corrosion resistance. This is due to the presence of iron nitrides and few chromium nitride phases. In this study an attempt is made to study the effect of alloying elements on the corrosion properties of EN 8 (AISI 1045), En 24 (AISI 4340), AISI H13 and AISI 304 steels during plasma nitriding.