Microstructure and dry sliding wear resistance evaluation of plasma nitrided austenitic stainless steel type AISI 316LN against different sliders

In this work, Plasma Nitriding was carried out at a temperature of 570 degrees C on nuclear grade austenitic stainless steel type AISI 316 LN (316LN SS) in a gas mixture of 20% N-2-80% H-2 to improve the surface hardness and thereby sliding wear resistance. The Plasma Nitride (PN) treated surface has been characterized by Vickers microhardness measurements, Scanning Electron Microscopic (SEM) examination, X-ray Diffraction (XRD) and sliding wear assessment. The average thickness of the PN layer was found to be 70 mu m. Microhardness measurements showed a significant increase in the hardness from 210 HV25g (unnitrided sample) to 1040 HV25g (Plasma Nitrided sample). The XRD reveals that PN layer consists of CrN, Fe4N and Fe3N phases along with austenite phase. The tribological parameters such as the friction coefficient and wear mechanism have been evaluated at ambient conditions for PN treated ring (PN ring) vs. ASTM A453 grade 660 pin (ASTM pin), PN ring vs. Nickel based alloy hard faced pin (Colmonoy pin), PN ring vs. 316LN SS pin and 316LN SS ring vs. 316LN SS pin. The wear tracks have been analyzed by SEM, Energy Dispersive X-ray Analysis (EDX) and Optical Profilometry. The untreated 316LN SS ring vs. 316LN SS pin produced severe wear and was characterized by a combination of delamination and adhesion wear mechanism, whereas wear mechanism of the PN rings reveals mild abrasion and a transfer layer from pin materials. (C) 2012 Elsevier B.V. All rights reserved.

Interdiffusion and solid solution strengthening in Ni-Co-Pt and Ni-Co-Fe ternary systems

Diffusion couple experiments are conducted in Co-Ni-Pt system at 1200 degrees C and in Co-Ni-Fe system at 1150 degrees C, by coupling binary alloys with the third element. Uphill diffusion is observed for both Co and Ni in Pt rich corner of the Co-Ni-Pt system, whereas in the Co-Ni-Fe system, it is observed for Co. Main and cross interdiffusion coefficients are calculated at the composition of intersection of two independent diffusion profiles. In both the systems, the main interdiffusion coefficients are positive over the whole composition range and the cross interdiffusion coefficients show both positive and negative values at different regions. Hardness measured by performing the nanoindentations on diffusion couples of both the systems shows the higher values at intermediate compositions.

Fretting wear study of Cu-10 wt% TiB2 and Cu-10 wt% TiB2-10 wt% Pb composites

In developing materials with better tribological properties, it is always conceived that the addition of softer phase would result in better frictional behavior. In order to address this issue, we report here the results of fretting wear study on Cu-10 wt% TiB2 and Cu-10 wt% TiB2-10 wt% Pb composites, sintered using spark plasma sintering (SPS) technique. It was found out that the addition of softer phase i.e. 10 wt % Pb to Cu-10 wt% TiB2 composites has not resulted in the lowering of the coefficient of friction (COF). The combination of steady state COF (0.6) and wear rate (10(-3) mm(3)/N-m) was measured and such properties are even better than that obtained with TiB2 coatings reported in the literature. For Cu-10 wt% TiB2 sintered at different temperature, a lower wear resistance with increase in hardness is being measured. An attempt has been made to correlate the observed wear behavior with the surface and subsurface deformation. The formation of a wear-resistant delaminated tribolayer consisting of TiB2 particles and ultrafine oxide debris (Cu, Fe, Ti)(x)O-y was the reason assigned for the observed low wear rate of these composites. (C) 2013 Elsevier B.V. All rights reserved.

Microstructure-Wear Resistance Correlation and Wear Mechanisms of Spark Plasma Sintered Cu-Pb Nanocomposites

The dispersion of a softer phase in a metallic matrix reduces the coefficient of friction (COF), often at the expense of an increased wear rate at the tribological contact. To address this issue, unlubricated fretting wear tests were performed on spark plasma sintered Cu-Pb nanocomposites against bearing steel. The sintering temperature and the Pb content as well as the fretting parameters were judiciously selected and varied to investigate the role of microstructure (grain size, second-phase content) on the wear resistance properties of Cu-Pb nanocomposites. A combination of the lowest wear rate (similar to 1.5 x 10(-6) mm(3)/Nm) and a modest COF (similar to 0.4) was achieved for Cu-15 wt pct Pb nanocomposites. The lower wear rate of Cu-Pb nanocomposites with respect to unreinforced Cu is attributed to high hardness (similar to 2 to 3.5 GPa) of the matrix, Cu2O/Fe2O3-rich oxide layer formation at tribological interface, and exuding of softer Pb particles. The wear properties are discussed in reference to the characteristics of transfer layer on worn surface as well as subsurface damage probed using focused ion beam microscopy. Interestingly, the flash temperature has been found to have insignificant effect on the observed oxidative wear, and alternative mechanisms are proposed. Importantly, the wear resistance properties of the nanocomposites reveal a weak Hall-Petch-like relationship with grain size of nanocrystalline Cu. (C) The Minerals, Metals & Materials Society and ASM International 2013

In vitro/In vivo assessment and mechanisms of toxicity of bioceramic materials and its wear particulates

With the progress in modern technological research, novel biomaterials are being largely developed for various biomedical applications. Over the past two decades, most of the research focuses on the development of a new generation of bioceramics as substitutes for hard tissue replacement. In reference to their application in different anatomical locations of a patient, newly developed bioceramic materials can potentially induce a toxic/harmful effect to the host tissues. Therefore, prior to clinical testing, relevant biochemical screening assays are to be performed at the cellular and molecular level, to address the issues of biocompatibility and long term performance of the implants. Along with testing strategies in the bulk material toxicity, a detailed evaluation should also be conducted to determine the toxicity of the wear products of the potential bioceramics. This is important as the bioceramics are intended to be implanted in patients with longer life expectancy and notwithstanding, the material will eventually release finer (mostly nanosized) sized debris particles due to continuous wear at articulating surfaces in the hostile corrosive environment of the human body. The wear particulates generated from a biocompatible bioceramic may act in a different way, inducing early/late aseptic loosening at the implant site, resulting in osteolysis and inflammation. Hence, a study on the chronic effects of the wear particulates, in terms of local and systemic toxicity becomes the major criteria in the toxicity evaluation of implantable bioceramics. In this broad perspective, this article summarizes some of the currently used techniques and knowledge in assessing the in vitro and in vivo cytotoxicity and genotoxicity of bioceramic implant materials. It also addresses the need to conduct a broad evaluation before claiming the biocompatibility and clinical feasibility of any new biomaterial. This review also emphasizes some of the case studies based on the experimental designs that are currently followed and its importance in the context of clinical applications.

Cost-effective wear and oxidation resistant electrodeposited Ni-pumice coating

In the search for newer distributed phases that can be used in Ni-composite coatings, inexpensive and naturally available pumice has been identified as a potential candidate material. The composition of the pumice mineral as determined by Rietveld analysis shows the presence of corundum, quartz, mulllite, moganite and coesite phases. Pumice stone is crushed, ball-milled, dried and dispersed in a nickel sulfamate bath and Ni-pumice coatings are electrodeposited at different current densities and magnetic agitation speeds. Pumice particles are uniformly incorporated in the nickel matrix and Ni-pumice composite coatings with microhardness as high as 540 HK are obtained at the lowest applied current density. In the electrodeposited Ni-pumice coatings, the grain size of Ni increases with the applied current density. The overall intensity of texture development is slightly stronger for the Ni-pumice composite coating compared to plain Ni coating and the texture evolution is possibly not the strongest deciding factor for the enhanced properties of Ni-pumice coatings. The wear and oxidation resistances of Ni-pumice coating are commensurate with that of Ni-SiC coating electrodeposited under similar conditions. (C) 2014 Elsevier B.V. All rights reserved.

Interdiffusion and solid solution strengthening in Ni-Co-Pt and Ni-Co-Fe ternary systems

Diffusion couple experiments are conducted in Co-Ni-Pt system at 1200 degrees C and in Co-Ni-Fe system at 1150 degrees C, by coupling binary alloys with the third element. Uphill diffusion is observed for both Co and Ni in Pt rich corner of the Co-Ni-Pt system, whereas in the Co-Ni-Fe system, it is observed for Co. Main and cross interdiffusion coefficients are calculated at the composition of intersection of two independent diffusion profiles. In both the systems, the main interdiffusion coefficients are positive over the whole composition range and the cross interdiffusion coefficients show both positive and negative values at different regions. Hardness measured by performing the nanoindentations on diffusion couples of both the systems shows the higher values at intermediate compositions.

Effect of strain rate response and pin diameter on mechanically mixed layer formation and wear mechanisms in a Ti6Al4V-SS316L pair

Three mechanisms operate during wear of materials. These mechanisms include the Strain Rate Response (SRR - effect of strain rate on plastic deformation), Tribo-Chemical Reactions (TCR) and formation of Mechanically Mixed Layers (MML). The present work investigates the effect of these three in context of the formation of MML. For this wear experiments are done on a pin-on-disc machine using Ti64 as the pin and SS316L as the disc. It is seen that apart from the speed and load, which control the SRR and TCR, the diameter of the pin controls the formation of MML, especially at higher speeds.

Microstructure and wear resistance of in situ TiCp composite coating by laser cladding

A new in situ method was realized by one step laser cladding to produce Ni-base alloy composite coating reinforced by in situ reacted and gradiently distributed TiCp particles. The submicron TiCp particles were formed and uniformly distributed because of the in situ reaction and trapping effect under the rapid solidification condition. And, TiCp particles were of gradient distribution on a macro scale and their volume fraction increased from 1.86% at the layer/substrate interface to a maximum 38.4% at the surface of the layer. Furthermore, the in situ generated TiCp/gamma-Ni interfaces were free from deleterious surface reactions. Additionally, the clad coating also revealed a high microhardness of gradient variation with the layer depth and the superior abrasive wear resistance.

Effects of La2O3 on Microstructure and Wear Properties of Laser Clad gamma/Cr7C3/TiC Composite Coatings on TiAl Intermatallic Alloy

The effects of La2O3 addition on the microstructure and wear properties of laser clad gamma/C(r)7C(3)/TiC composite coatings on gamma-TiAl intermetallic alloy substrates with NiCr-Cr3C2 precursor mixed powders have been investigated by optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy-dispersive spectrometer (EDS) and block-on-ring wear tests. The responding wear mechanisms are discussed in detail. The results are compared with that for composite coating without La2O3. The comparison indicates that no evident new crystallographic phases are formed except a rapidly solidified microstructure consisting of the primary hard Cr7C3 and TiC carbides and the gamma/Cr7C3 eutectics distributed in the tough gamma nickel solid solution matrix. Good finishing coatings can be achieved under a proper amount of La2O3-addition and a suitable laser processing parameters. The additions of rare-earth oxide La,03 can refine and purify the microstructure of coatings, relatively decrease the volume fraction of primary blocky Cr7C3 to Cr7C3/gamma eutectics, reduce the dilution of clad material from base alloy and increase the microhardness of the coatings. When the addition of La2O3 is approximately 4 wt.%, the laser clad composite coating possesses the highest hardness and toughness. The composite coating with 4 wt.%La2O3 addition can result the best enhancement of wear resistance of about 30%. However, too less or excessive addition amount of La2O3 have no better influence on wear resistance of the composite coating.

Thermal Residual Stresses in Particulate Composites and Its Toughening Effect

In this paper, an accurate formula for calculating the thermal residual stress field in a particle-reinforced composite are presented. Numerical examples are given to show r-variations of the thermal residual stresses. The increase in fracture toughness of matrix predicted by the thermal residual stress field is compared well with the experimentally measured increase.

Friction and Wear Studies of Octadecyltrichlorosilane SAM on Silicon

A self-assembled monolayer of octadecyltrichlorosilane (OTS) was prepared on a single-crystal silicon wafer (111) and its tribological properties were examined with a one-way reciprocating tribometer. The worn surfaces and transfer film on the counterface were analyzed by means of scanning electron microscopy and X-ray photoelectron spectroscopy. The results show that, due to the wear of the OTS monolayer and the formation of the transfer film on the counterpart ball, the friction coefficient gradually increases from 0.06 to 0.13 with increasing sliding cycles and then keeps stable at a normal load of 0.5N. The transfer film is characterized by deposition, accumulation, and spalling at extended test duration. Though low friction coefficients of the monolayer in sliding against steel or ceramic counterfaces are recorded, poor load-carrying capacity and antiwear ability are also shown. Moreover, the monolayer itself or the corresponding transfer film on the counterface fails to lubricate even at a normal load of 1.0 N. Thus, the self-assembled monolayer of octadecyltrichlorosilane can be a potential boundary lubricant only at very low loads.

The mechanical properties of an aluminum alloy by plasma-based ion implantation and solution-aging treatment

The age-strengthening 2024 aluminum alloy was modified by a combination of plasma-based ion implantation (PBII) and solution-aging treatments. The depth profiles of the implanted layer were investigated by X-ray photoelectron spectroscopy (XPS). The structure was studied by glancing angle X-ray diffraction (GXRD). The variation of microhardness with the indenting depth was measured by a nanoindenter. The wear test was carried on with a pin-on-disk wear tester. The results revealed that when the aluminum alloys were implanted with nitrogen at the solution temperature, then quenched in the vacuum chamber followed by an artificial aging treatment for an appropriate time, the amount of AIN precipitates by the combined treatment were more than that of the specimen implanted at ambient temperature. Optimum surface mechanical properties were obtained. The surface hardness was increased and the weight loss in a wear test decreased too.

Strengthening Mechanisms And Dislocation Dynamics In Twinned Metal Nanowires

Microtwins are frequently observed in face-centered-cubic (fcc) metal nanowires with low stacking fault energy. The authors have previously reported that the tensile Yield strength of copper nanowires can be increased by, the presence of twin boundaries. lit this work, simulations are carried out under both uniaxial tension and compression loading, to demonstrate that the strengthening effects are inherent to these nanowires, independent of the loading condition (tensile/compressive). It appears that the strengthening mechanism of the twinned nanowires can be attributed to stress redistribution due to the change of crystallographic orientations across twin boundaries, which requires larger external stress to make them Yield as compared to the twin-free wire.