Friction and wear of non-ferrous metals and coatings are of considerable interest in the light of use of the above in tribo-contacts. As most of the mechanisms governing the seizure of materials are concentrated at the center of the contact and are hidden, it is difficult to observe any precipitate changes in the behavior of such materials using conventional tools. In this work, we have used an X-ray microscope for in-situ observation of frictional seizure, wear and interfacial features during the testing of aluminium (AA1100) specimens sliding against Al 6061 disk. This technique enables the observation of interfacial features of the hidden contact despite the small density differences that exist between the sliding pair of materials. Seizure tests were conducted at different sliding speeds of 2 and 4 m/s. Aluminium was found to undergo incipient melting during sliding at a sliding speed of 2 m/s whereas the specimen tested at 4 m/s was found to undergo a severe plastic distortion thus restricting further testing of the same. Frictional heating of concentrated spots resulted in melting wear and diffusion assisted bonding of surface layers. This was later found to develop into a conformal contact following a lumpy transfer of material. The mechanisms of seizure and wear were affected by the sliding speeds during testing. At lower sliding speed (2 m/s) the transfer and bonding of deposits occurred due to direct contact of nascent sliding surfaces.

Artificial joints in orthopedics occupy a principal position owing to the increase in number of cases suffering from arthritis and associated diseases in addition to impairment caused by accidents. In this work, one of the most commonly used joint material, i.e. ultrahigh molecular weight polyethylene (UHMWPE), was tested against the duplex stainless steels instead of the conventional 316 L stainless steel. The UHMWPE was found to exhibit the lowest friction coefficient and wear rates when lubricated with water followed by globulin and glucose. The friction coefficient in the presence of egg albumen was higher along with high wear rates recorded. Post-test evaluation of surface roughness and wear scar/track analysis was performed to identify the wear mechanisms. Worn surfaces were analyzed using a differential scanning calorimeter for changes in crystallinity with sliding. The specimens tested under lubricated conditions with glucose, egg albumen and globulin indicated the presence of reaction products on the worn surface. Adhesive and corrosive wear mechanisms were the predominant modes of wear identified on the polymer samples. The wear tracks indicated that the proteins did react with the counterface material forming a thin deposit on them. Low temperature nitriding of the duplex stainless steel counterfaces were performed and the UHMWPE specimens were tested under similar conditions against the nitrided surfaces. Low temperature nitriding of the counterface did result in improved tribological behavior of UHMWPE and the corrosive effects were minimal.

Diamond films were prepared on a pure Ti substrate using the microwave plasma assisted chemical vapor deposition (MW-PACVD) method. The effects of applying two types of gas mixtures (H2/CH4 and Ar/H2/CH4) during diamond deposition on the microstructure of a Ti substrate were studied. With H2/CH4 (196:4) gas mixture, during diamond film deposition, hydrogen diffused into the Ti substrate and led to significant microstructure coarsening and a severe loss in Charpy impact energy. Post dehydrogenation annealing at a temperature of 800°C, could not change the coarse structure of the substrate, thus there was no improvement in Charpy impact energy. With the application of Ar/H2/CH4 (180:16:4) gas mixture, a smooth and nano-crystalline diamond film was deposited, and there was a minimum change in the substrate microstructure and Charpy impact energy after diamond deposition. The above results provide useful information for the successful application of diamond films (on a Ti substrate) for biomedical and aerospace application.

Amorphous carbon nitride (CNx) films were deposited on plasma nitrided Ti–6Al–4V substrate in order to improve the adhesion strength and tribological behaviour. Scratch and ball-on-disk wear tests were performed to evaluate the load bearing capacity, wear and friction characteristics of the duplex-treated coatings. Compared with a CNx film deposited on Ti–6Al–4V substrate, the load bearing capacity of a CNx film deposited on plasma nitrided layer was improved dramatically. Results showed that under dry sliding condition, the duplex-treated system was more effective in maintaining a favourable low and stable coefficient of friction and improving the wear resistance than both individual plasma nitriding and CNx film on Ti–6Al–4V substrate. The reasons for this significant improvement in tribological behaviour with the application of duplex treatment can be attributed to the combined benefits from both plasma nitriding and CNx films. (1) Plasma nitriding of Ti–6Al–4V produces a graded hardened case which serves as an excellent supporting and load bearing layer for hard CNx films. (2) The CNx film deposited at low temperature can produce a wear resistant and low-friction surface without impairing the beneficial effects from plasma nitriding treatment, and the smooth CNx films could effectively reduce both the interfacial stresses and the stresses near the surface thus providing a good tribological behaviour. (3) The graphitisation of the wear debris during dry sliding condition can help to decrease the coefficient of friction and improve the wear resistance.

Observation of frictional contacts has always been a problem as the contact is normally hidden. In this work, an X-ray microscope has been used for in situ observation of frictional seizure, wear and interfacial features during the testing of mild steel specimens sliding against an Al alloy 6061 disc. This technique enables the interfacial features of the hidden contact to be observed. Seizure tests were conducted at different sliding speeds of 2, 4 and 5 m/s under lubricated conditions with plain mineral oil. The images obtained during the tests indicated that the X-ray attenuation along its path increased with sliding at isolated locations, due possibly to localized changes in path length or attenuation by the degraded mineral oil. The sliding speed was found to have a considerable impact on the degradation of the oil, which affected the seizure behaviour.

Diamond coatings appear to be a promising solution for the improvement of tribological behavior of titanium alloys. By means of microwave plasma assisted chemical vapor deposition (MW-PACVD), diamond coating was deposited on pure titanium using CH4/H-2 gas mixtures under different plasma powers. Surface and interface characterization of the deposited coating under different plasma powers was carried out using SEM, grazing incidence x-ray diffraction (GIXD) and Raman spectroscopy. Adhesion of diamond coating with substrate was evaluated using an indentation tester. Results showed that adhesion of diamond coatings was not good under high plasma power, whereas the crystallinity of diamond coating was not good under low plasma power. The higher the plasma power, the larger the diamond crystal size, the less content of non-diamond carbon and the poorer the adhesion strength. During the diamond deposition, growth of TiC competed with diamond formation for the available carbon content. Relatively low plasma power inhibited TIC formation more than diamond formation. Under a high plasma power, the formation of a thick and porous TiC layer appeared to promote interfacial debonding and spallation of the diamond coating.

Observation of frictional contacts has always been a problem for long as the contact is normally hidden. In this work, we have used an X-ray microscope for in-situ observation of frictional seizure, wear and interfacial features during the testing of mild steel specimens sliding against Al 6061 disk. This technique enables the observation of interfacial features of the hidden contact. Seizure tests were conducted at different sliding speeds of 2, 4 and 5 m/s. The images obtained during the tests indicated that the wear process was a combination of random transfer events and cyclic process of a close contact followed by a partial separation of the sliding surfaces. Wear was concentrated over a certain specific area during the initial part of the test but later the contact developed into a conformal contact following a lumpy transfer of material. The mechanisms of seizure and wear were affected by the sliding speed. At a sliding speed of 4 and 5 m/s, the transfer and bonding of material was not directly caused by nascent surface contact but due to contact of rolled and compacted wear debris with the nascent surfaces. Whereas at lower sliding speed (2 m/s) the transfer and bonding of deposits occurred due to direct contact of nascent sliding surfaces.

Titanium alloys are widely used in aerospace and biomedical conditions, however, they are notorious for the poor tribological properties. The deposition of a well adherent diamond coating is a promising way to solve this problem. In this study, diamond coatings were deposited on pure titanium using microwave plasma assisted chemical vapour deposition (MW-PACVD). Characterisation of diamond coatings was performed using scanning electron microscopy (SEM), laser profilometry, Raman spectroscopy, grazing incidence X-ray diffraction (GIXD) and atomic force microscopy (AFM). Tribological properties of diamond coatings were evaluated using a ball-on-disk wear tester (sliding with Al2O3 balls) and a scratch tester (sliding with diamond pin). Results showed that the friction and wear properties of polycrystalline diamond coatings as well as the wear of the counterface were dependent significantly on the surface roughness, the morphology and crystalline structure of diamond coatings as well as the counterface materials. For (111)-textured diamond coatings with rough surface and sharp asperities sliding with Al2O3 balls, the coefficient of friction was much higher than that of (100)-textured coatings, and the wear of the counterface material was quite high. After polishing the diamond coating, the surface roughness, coefficient of friction and wear of counterface decreased significantly. If sliding with diamond pins, the coefficient of friction of diamond coating shows a quite low and stable value. To improve the tribological properties, a three-step deposition method was proposed to obtain a smooth and nano-crystalline diamond layer on bulk diamond coatings. The so-formed diamond coating showed the highest load bearing capacity, the lowest coefficient of friction and the lowest wear of the counterface.

During diamond deposition on a titanium substrate using a gas mixture of H 2 –CH 4 (196 : 4), hydrogen easily diffused into the substrate and led to significant microstructural coarsening and a severe loss in Charpy impact energy. In order to prevent the rapid diffusion of hydrogen into the substrate during diamond deposition, three techniques were studied. The first method was to use a post-vacuum annealing treatment to achieve dehydrogenation of a diamond coated titanium specimen. However, the Charpy impact energy could not be restored significantly even after a few hours of annealing. The second method was to apply a barrier interlayer between the diamond coating and titanium substrate. Results showed that even though the sputtered TiN coating and plasma nitrided layer could prevent the rapid diffusion of hydrogen and carbon into the titanium substrate, the deposited diamond coatings had poor adhesion to the substrate. A graded interlayer produced by plasma nitriding followed by plasma carbonitriding was effective in preventing the rapid diffusion of hydrogen and also improving the nucleation rate and adhesion of the diamond coating. The third method was to use a gas mixture of Ar–H 2 –CH 4 instead of the conventional H 2 –CH 4 . With the use of an Ar–H 2 –CH 4 (180 : 16 : 4) mixture, a smooth and nanocrystalline diamond coating was deposited, and there was little change in the substrate microstructure or Charpy impact energy after diamond deposition.

To increase diamond nucleation rate and prevent the rapid diffusion of hydrogen and carbon into Ti substrate during diamond deposition, different interlayers were studied in this paper. Results showed that on TiN interlayer, there was no significant improvement in diamond nucleation and growth, and the deposited diamond coatings showed poor adhesion. There were two mechanisms for diamond nucleation on diamond-like-carbon (DLC) interlayer. DLC film was etched by hydrogen plasma and changed to diamond crystals. At the same time, new diamond crystals were formed on the DLC interlayer in which DLC acted as the precursor for diamond nucleation. However, the so-formed diamond coating had poor adhesion strength. A graded interlayer combining plasma nitriding followed by plasma carbonitriding was effective in preventing the rapid diffusion of hydrogen and carbon into the substrate and improving the nucleation rate and adhesion of diamond coating.

Hard chromium nitride films were deposited by ion-beam-enhanced-deposition (IBED) technique. The effects of ion beam energy and ion beam current on microstructure and mechanical properties of IBED CrN films were studied, and the optimized parameters were found to prepare the films to improve the fretting wear resistance of Ti–6Al–4V. The fretting wear behavior of the IBED CrN film was evaluated using a ball-on-flat system under unlubricated conditions, and the results were compared with those of PVD CrN films. Results showed that both the bombardment energy and ion beam current had significant effects on the microstructure, preferred orientation, hardness and adhesion strength of the IBED CrN thin films. The Fretting wear resistance of IBED CrN films was better than those of PVD CrN films due to a dense and fine microstructure, good adhesion strength, deep hardening depth, etc. Fretting parameters (normal load and amplitude) played an important role in the transition of the fretting regime (from partial slip to gross slip regime). Oxidation and abrasive wear were the main fretting wear mechanisms for IBED CrN film.

Titanium alloys are characterized by poor tribological properties, and the traditional use of titanium alloys has been restricted to nontribological applications. The deposition of a well adherent diamond coating is a promising way to solve this problem. In this study, the tribological properties of diamond-coated titanium were studied using a pin-on-disk tribometer, and the results were compared with those of pure titanium and plasma nitrided titanium. The tribological behavior of pure titanium was characterized by high coefficient of friction and rapid wear of materials. Plasma nitriding improved the wear resistance only under low normal load; however, this hardened layer was not efficient in improving the wear resistance and the friction properties under high normal load. Diamond coating on pure titanium improved the wear resistance of titanium significantly. Surface profilometry measurement indicated that little or no wear of the diamond coating occurred under the test conditions loads. The roughness of the diamond coating was critical because it controlled the amount of abrasive damage on the counterface. Reducing the surface roughness by polishing led to the reductions in both the friction and wear of the counterface.

Diamond coatings appear to be a promising solution for the improvement of tribological behavior of titanium alloys. By means of microwave plasma assisted chemical vapor deposition (MW-PACVD), diamond coating has been deposited on pure titanium substrates using CH4/H2 mixtures at moderate temperature (550–600°C). The surface and interface characterization of deposition coating with increasing deposition duration up to 21h has been studied using SEM and grazing incidence X-ray diffraction (GIXD). TiC formation on the substrate surface was detected after 15min deposition. Growth of TiC competed with diamond formation for the available carbon. The formation of a thick porous TiC layer appeared to promote interfacial debonding and spallation of the diamond coating. During the deposition of diamond coatings, hydrogen diffused into Ti substrate, and the formation of titanium hydride was detected by GIXD. The formation of TiC and diamond layers did not inhibit the formation of titanium hydride. This led to profound microstructural changes and a severe loss of impact strength. A two-step process with higher ratio of CH4 during the first step deposition appeared to be beneficial as a result of the higher nuclei density of diamond crystals. The diamond coating so formed was observed to be in more intimate contact with the substrate.

It is well documented that plasma nitrided steels exhibit superior fatigue resistance by virtue of induced compressive residual stress. In the present paper, six steels with different alloying elements and contents were plasma nitrided for 4 and 9 h at 580°C. These were then analysed in terms of microstructural features, microhardness profiles, and residual stress distribution. A Philips X-ray diffractometer was used for phase determination and residual stress measurement. The paper discusses the use of X-ray diffractometry to measure residual stress, emphasising the significance of K calibration, choice of ψ angle, and validation of 2θ measurement. Results showed a close relationship between microhardness profiles and residual stress distribution. Effects of the various alloying elements such as Cr, Al, Ti, W, and V were explored in terms of their plasma nitrided microstructural features as well as their contribution to surface hardness and case depth.

The probability of encountering fretting in machines and engineering structures is extremely high, and it is well known that aluminum alloys have poor fretting wear resistance. In this investigation, effect of laser surface alloying of Ni, Cr on the fretting resistance of 6061 aluminum alloys under unlubricated conditions was studied. The fretting wear performance of the laser treated alloys was characterized by evaluating the wear volume loss, the coefficient of friction and fretting mechanisms. It was found that the fretting wear resistance of 6061 aluminum alloy was improved by a factor of 3 after laser alloying while the coefficient of friction was decreased. In situ observation of fretting wear was performed by means of X-ray imaging (real time radiography) in this investigation. The obtained X-ray images and SEM post-observation of the fretting scar indicated that the fretting wear process of laser treated specimens was a combination of adhesive, abrasive, oxidation and delamination wear. The mechanisms during the running-in period are adhesive and abrasive wear. During prolonged running, delamination and oxidation were the main wear mechanisms for both laser treated and untreated specimen.

Metal-matrix composites (MMCs) have been shown to achieve superior mechanical properties compared with those of the respective unreinforced alloys. However, only limited information on creep of aluminium-based cast MMCs have been published. All the published papers followed the classical methods of creep testing i.e. samples were tested at a constant load and temperature till failure. Under real service conditions, a component might be faced with a constant service temperature, but would normally be also subjected to load changes during its service life. This paper proposes a model for creep of the A359/SiC/10p MMC subjected to cumulative loading. The paper also reports the results of cumulative creep experiments conducted and compares them with the proposed model. Preliminary results showed that an acceptable level of accuracy could be achieved using the optimum values for the cumulative creep indices. By establishing the creep lives of a material at different loading conditions, calculations can be made by the proposed model for an estimation of the material's creep life when subjected to a step-wise loading condition.

Detailed wear and friction phenomena are usually hidden between the two contacted surfaces. Direct or in-situ observation of wear process is supposed to obtain some time-dependent changes and shed more light on the real wear and friction mechanisms. In this paper, X-ray imaging, one of the advanced tools for modern non-contact and non-destructive inspection, was applied to observe in-situ the fretting wear processes of a laser-alloyed coatings and plasma-sprayed hydroxyapatite (HA) coatings against stainless steel under unlubricated conditions. X-ray images clearly showed the contact nature, the wear process, the formation and compaction of wear debris, spallation of the coatings, large-scale removal of materials, crack formation and propagation, etc. According to the analysis of X-ray images, the fretting wear process of laser-treated specimens was a combination of adhesive, abrasive, oxidative and delamination wear; and the fretting wear mechanisms for the plasma-sprayed HA coating were mainly delamination and abrasive wear. It can be concluded that X-ray imaging is a promising method for the in-situ observation of wear processes and deterioration mechanisms of coatings under fretting conditions.

This paper reports the results of research conducted on creep properties of the cast A359/SiC/XXp system. The effect of percentage volume fraction of SiC particulate (SiCp) reinforcement on the creep of the composite was bench-marked against the unreinforced A359 alloy. The properties of the as-cast A359 alloy, A359/SiC/10p and A359/SiC/20p were evaluated at three temperatures. Results show that as the volume fraction of SiCp reinforcement increased, resistance to creep increased and subsequently creep life increased. Creep life results corresponded to the increase in tensile strengths of the material being tested. In this study, tensile strength properties resulted in an increase with the increment of percentage volume fraction reinforcement. From the creep data, the creep exponents and activation energies of the materials were calculated and reported in this paper. It is shown that the reinforced alloy systems exhibit a low strain rate and high apparent activation energy for creep deformation compared to that of the unreinforced alloy.

Martensitic stainless steel. AISI 410 was surface hardened by plasma nitriding for enhancement of its wear properties. Wear tests were carried out on plasma nitrided 410 stainless-steel specimens under dry-sliding and lubricated conditions at room temperature, using a pin-on-cylinder wear-testing rig. Mineral oil. Mobil Super 2T, and synthetic oil, Mobil 1, were used as the lubricants. Results showed that the friction coefficient of 410 stainless steel was decreased and the wear resistance was increased significantly after plasma nitriding. Both mineral oil and synthetic oil were effective in controlling the friction and wear of nitrided 410 stainless steel as well as temperature rise during sliding. Synthetic oil was found to be superior to mineral oil especially under high sliding speeds and loads. X-ray imaging was used to inspect the worn specimen. The wear mechanisms for both untreated and nitrided specimens were mainly adhesion and delamination.