Tribological Potential Research Articles

Microfracture and Limited Tribochemical Wear of Silicon Carbide During High‐Speed Sliding in Cryogenic Environment

In an effort to develop an understanding of the tribological properties of silicon carbide (SiC) in a cryogenic environment, this contribution reports on the results of the sliding wear properties of the self‐mated SiC in liquid nitrogen (LN2). Two sets of sliding wear tests were conducted in a planned manner in LN2 under varying combinations of operating conditions, using a specially designed high‐speed cryo‐tribometer. In the first set, the sliding velocity is varied up to 1.1 m/s, for 600 s, at a constant load of 5 N; while the second set of experiments were conducted with loads of 5, 10, and 15 N, at a constant speed of 3.3 m/s for 900 s, thereby enabling to evaluate tribological potential over a broad spectrum of operating conditions. In our experiments, high coefficient of friction (COF) (0.28–0.40) and high wear resistance (∼10−7–10−6 mm3/N m) have been measured for self‐mated SiC. The topographical observations using a scanning electron microscope reveal that limited tribochemical layer formation, as well as grain boundary microfracture‐induced damage mechanisms, contribute to the wear of self‐mated SiC. The experimental results are critically analyzed with reference to flash temperature and contact stress conditions, as well as compared with some baseline experiments, conducted under ambient conditions. A comparison with our earlier research results, obtained with self‐mated Al2O3 or ZrO2, establishes the good tribological potential of self‐mated SiC in LN2, in terms of exhibiting a better combination of COF and wear rate.

An investigation of the wear behaviour of 0.2% C dual phase steels

In order to explore the tribological potential of the dual phase (DP) steel as wear resistant material, the wear characteristics of this steel have been investigated and compared with those observed in plane carbon normalized (N) steel that has the same composition of 0.2 wt% carbon. Dry sliding wear tests have been carried out using a pin-on-disk wear testing machine at normal loads of 61.3, 68.5, 75.7 and 82.6 N and at a constant sliding velocity of 1.20 m/s. At these loads, the mechanism of wear is mainly delamination, which has been confirmed by SEM micrographs of surface, subsurface and wear debris of samples. The wear rate of the DP steel and N steel have been explained with respect to microstructure and the wear mechanism.

Mild Oxidative Wear Behaviour of Plain Carbon Dual‐Phase Steel

In order to explore the tribological potential of the dual phase (DP) steel as wear resistant material, the wear and friction characteristics of this steel, which consists of hard martensite island embedded in a ductile ferrite matrix, were investigated and compared with those observed in plain carbon normalized (N) steel with the same composition of 0.2 wt pct carbon. Dry sliding wear tests were carried out using a pin‐on‐disk wear testing machine at normal loads of 21.3, 28.5, 35.7 and 42.6 N and at a constant sliding velocity of 1.20 m/s. The analysis of surface and wear debris of the tested specimens showed that wear mechanism was mainly mild oxidative. The friction and wear rate of the DP steel and N steel were explained with respect to microstructure and the wear mechanism.

Dry Sliding Oxidative Wear in Plain Carbon Dual Phase Steel

To investigate the tribological potential of the dual phase (DP) steel as a wear resistant material, the wear and the friction characteristics of this steel, which consists of hard martensite islands embedded in a ductile ferrite matrix, have been investigated and compared with those observed in plain carbon hardened (H) steel that has the same carbon content of 0. 2%. Dry sliding wear tests have been carried out using a pin-on-disk wear testing machine at different normal loads of 21. 3 N, 28. 5 N, 35. 7 N, and 42. 6 N and at a constant sliding velocity of 1. 20 m/s. The analysis of surface and wear debris of samples showed that the wear mechanism was mainly mild oxidative. The friction and the wear rate of the H steel and the DP steel have been explained with respect to the microstructure and the wear mechanism.

Effect of microstructure on the oxidative wear behavior of plain carbon steel

According to explore the tribological potential of the dual phase (DP) steel as wear resistant material, the wear and friction characteristics of this steel, which consists of hard martensite island embedded in a ductile ferrite matrix, have been investigated and compared with those observed in plane carbon normalized (N) and hardened (H) steels with the same composition of 0.2 wt.% carbon. Dry sliding wear tests have been conducted using a pin-on-disk machine under different normal loads of 21.3, 28.5, 35.7 and 42.6 N and at a constant sliding speed of 1.20 m/s. The analysis of surface and wear debris of specimens showed that wear mechanism was mainly mild oxidative. The friction, wear rate and wear coefficient of the steels, have been explained with respect to microstructure and the wear mechanism.

Correlating microstructural features with wear resistance of dual phase steel

In order to explore the tribological potential of the dual phase (DP) steel as a wear resistant material, the wear characteristics of the dual phase (DP) steel have been investigated with varying amounts of martensite from 43 to 81 vol pct, developed by varying holding time at the intercritical annealing temperature of 780 °C. Dry sliding wear tests have been conducted on DP steels using a pin-on-disk machine under different normal loads of 61.3, 68.5, 75.7 and 82.6 N and at a constant sliding speed of 1.20 m/s. At these loads, the mechanism of wear is mainly delamination, which has been confirmed by SEM micrographs of the subsurface and wear debris of the samples. Wear and friction properties have been found to be improved with increasing martensite volume fraction in dual phase steels.

Tribological properties of TiB 2 and TiB 2–MoSi 2 ceramic composites

Recently, dense monolithic TiB 2 and TiB 2–20 wt.% MoSi 2 composites with high hardness (24–26 GPa) have been processed by hot pressing. To assess the tribological potential, the present study was performed in analyzing the influence of load on the fretting wear of TiB 2 and TiB 2–MoSi 2 composites against bearing steel. Under the investigated conditions, a higher coefficient of friction (COF) of 0.5–0.6 was recorded with all the materials with a lower COF at a higher load of 10 N. Detailed microstructural investigation of the worn surfaces was carried out using SEM–EDS and XRD in order to understand the fretting wear mechanisms. Severe wear (order of 10 −5 mm 3/N m) was measured for the investigated materials under the selected fretting conditions with lower wear rate for TiB 2–20 wt.% MoSi 2 composite at all loads (2–10 N). While abrasive wear dominates the material removal process in the case of monolithic TiB 2, the tribochemical wear is observed to be the predominant wear mechanism for the composite.

Effect of martensite content on friction and oxidative wear behavior of 0.42 Pct carbon dual-phase steel

In order to explore the tribological potential of the dual-phase (DP) steel as a wear-resistant material, the friction and wear characteristics have been investigated for this steel with varying amounts of martensite from 42 to 72 vol pct, developed by varying holding time at the intercritical annealing temperature of 740 °C. Dry sliding wear tests have been conducted on DP steels containing 0.42 wt pct carbon using a pin-on-disk machine under different normal loads of 14.7, 19.6, 24.5, 29.4, and 34.3 N and at a constant sliding speed of 1.15 m/s. Weight loss has been measured at different time intervals on the same specimen. The variation of cumulative volume loss with sliding distance has been represented by two linear segments signifying the run-in and the steady state of wear. The mechanism of wear is primarily oxidative in nature, which has been confirmed by X-ray diffraction patterns of the wear debris generated during sliding. The wear rate varies linearly with load in both the run-in and the steady state. The wear rate decreases linearly with increasing volume fraction of martensite in DP steels reflecting the effect of hardness imparted by the increasing amount of martensite, which is a hard and load bearing phase. The average coefficient of friction also decreases linearly with increasing load as well as with increasing martensite volume fraction. In the run-in stage, the wear coefficient does not change significantly between DP1 and DP2 steels containing 42 and 51 vol pct martensite, respectively, but decreases sharply as one moves from DP2 to DP4 containing, respectively, 51 and 72 vol pct martensite. But in the steady state, the wear coefficient decreases almost linearly with increasing volume fraction of the martensite. The decrease in wear coefficient may be attributed to the decreasing wear rate dominating over the decrease in real area of contact due to increasing hardness.

The tribological potential of CrN and Cr(C,N) deposited by multi-arc PVD process

Ceramic coatings have been proven to be a good choice for preventing the base material from wear, corrosion, erosion and other unfavourable damage. In the field of thin solid films (< 10 μm), titanium nitride (TiN) is still the most widely accepted in engineering applications. Over the last years, chromium-base (Cr-base) coated tools have come onto the market. Consequently, deeper knowledge of Cr-base coatings is indeed required. Therefore, we conducted a series of experiments to assess the potential of chromium nitride (CrN) and chromium carbonitride (Cr(C,N) coatings. For comparison, TiN was also studied under identical conditions. The results showed that the surface micro-hardness of 10 μm CrN was the highest and the tribological performance of CrN and Cr(C,N) was excellent. Thus, CrN is expected to have potential to replace TiN in terms of wear resistance.

An investigation of the tribological potential of TiN, CrN and TiN + CrN physical vapor deposited coatings in machine element applications

This study investigates, through wear testing, the potential for carburized and tufftrided surface treated steels and the TiN, CrN and TiN + CrN physical vapor deposited (PVD) surface treatments to be used in the screw and rollers of the variable lead screw transmission mechanism (VLSTM). Indentation test results reveal that the thicker the PVD CrN coating, the lower is its adhesive strength, with the desired coating thickness being 10 μm. In general, all sliding pairs possess the best wear resistance under cutting fluid lubrication. Surface treated steels (upper moving specimen) paired with PVD coated parts possess very poor wear resistance under base oil lubrication, even worse than under dry wear. Suitable sliding pairs for VLSTM applications include: surface treated steels paired with either SKH51 or PVD coated specimens under cutting fluid lubrication; PVD coated specimens paired with SKH51 specimens under cutting fluid lubrication; and PVD coated specimens paired with PVD coated specimens under base oil and cutting fluid lubrication.

Friction and wear behavior of a number of ceramic-coated steels matched as sliding pairs to various surface-treated steels

Ceramic-coated steels (WC+12%Co and Cr3C2 + 25%NiCr applied by continuous detonation spraying, and Cr2O3 applied by plasma spraying) were mated as sliding pairs to surface-treated steels (case hardened, tufftrided) under both dry wear and lubricated conditions in order to assess their tribological potential. Under dry wear conditions, WC-Co demonstrates the lowest coefficient of friction but surface-treated steels paired with Cr3C2-NiCr possess the best wear resistance under both dry wear and lubricated conditions. Five different types of generalized friction behavior were identified among the pairs studied. Under dry wear conditions, the worn surface of Cr3C2-NiCr is covered with continuous and “island”-transferred layers, while that of Cr2O3 exhibits numerous cracks. The worn surface of WC-Co can be divided into four distinct regions, each possessing a major wear characteristic in addition to that of surface polishing. Wear mechanisms for TF1 surface-treated steels include surface polishing, strain fatigue and fracture of the work-hardened layer, while those for carburized steel include surface polishing, plastic deformation, material transfer and pile-up of back-transferred material. Under lubricated conditions, the amount of material transferred is reduced.

Ion implantation as an efficient surface treatment

Ion beam processing has for several years been well established in the semiconductor industry. In recent years ion implantation of tool steels, ceramics and even plastics has gained increasing industrial awareness. The development of ion implantation to a commercially viable surface treatment of tools and spare parts working in production type environments is very dependent on technical merits, economic considerations, competing processes and highly individual barriers to acceptance for each particular application. Some examples of this will be discussed. The development of the process is very closely linked with the development of high current accelerators and their ability to efficiently manipulate the samples being treated, or to make sample manipulation superfluous by using special beam systems like the PSII. Furthermore, the ability to produce high beam currents (mA) of a wide variety of ions is crucial. Previously, it was broadly accerted that ion implantation of tools on a commercial basis generally had to be limited to nitrogen implantation. The development of implanters which can produce high beam currents of ions like B+, C+, Ti+, Cr+ and others is rapidly changing this situation, and today an increasing number of commercial implantations are performed with these ions although nitrogen is still successfully used in the majority of commercial implantations. All in all, the recent development of equipment makes it possible to a higher extent than before to tailor the implantation to a specific situation. The emerging new possibilities in this direction will be discussed, and a broad selection of practical examples of ion implantation at standard low temperatures of tools and spare parts will be given. Furthermore, very interesting results have been obtained recently by implanting nitrogen at elevated temperatures, which yields a relatively deep penetration of the implanted ions. Besides various examples of direct ion implantation, the very cost-effective variation based on ion bombardment of the sample surfaces in a controlled atmosphere of oil vapour will be discussed and compared to recent investigations of high dose carbon implantations. Direct nitrogen implantation and implantation combined with nitriding of aluminium have both shown interesting tribological potential. Other and relatively now practical examples of ion implantation used for changing the tribological and other surface characteristics of ceramics and plastics will also be discussed.