Peter J. Blau

Galling is a severe form of surface damage in metals and alloys that typically arises under relatively high normal force and low sliding speed and in the absence of effective lubrication. It can lead to macroscopic surface roughening and seizure. The occurrence of galling can be especially problematic in high-temperature applications like diesel engine exhaust gas recirculation system components and adjustable turbocharger vanes, because suitable lubricants may not be available, moisture desorption promotes increased adhesion, and the yield strength of metals decreases with temperature. Oxidation can counteract these effects to some extent by forming lubricative oxide films. Two methods to improve the galling resistance of titanium alloy Ti-6Al-4V were investigated: (a) applying an oxygen diffusion treatment and (b) creating a metal–matrix composite with TiB₂ using a high-intensity infrared heating source. A new oscillating three-pin-on-flat, high-temperature test method was developed and used to characterize galling behavior relative to a cobalt-based alloy (Stellite 6B, HP Alloys, Windfall, IN). The magnitude of the oscillating torque, the surface roughness, and observations of surface damage were used as measures of galling resistance. Due to the formation of lubricative oxide films, the galling resistance of the Ti alloy at 485°C, even nontreated, was considerably better than it was at room temperature. The infrared (IR)-formed composite displayed reduced surface damage and lower torque than the substrate titanium alloy.

Ceramic particles, such as SiC and Al2 O3 , have been used to reinforce Al alloys to improve their strength and wear-resistance. However, previous studies mainly dealt with either relatively large hard particles (from tens to hundreds of micrometers in diameter) or nanometer-sized particles with low volume fractions (a few percent). In this study, near-fully-dense (97–99%) Al2 O3 -Al nanocomposites with higher particle concentrations (5–15 vol%) were processed using mechanical alloying and hot isostatic pressing. Transmission electron microscopy revealed very high dislocation density in aluminum matrix for these Al2 O3 -Al nanocomposites. High strength (σ0.2% : ∼500 MPa) and encouraging tribological properties have been observed. The Al2 O3 (15 vol%)-Al nanocomposites performed unexpectedly well when sliding against 52100 bearing steel. The friction coefficient of the nanocomposite was 55%, 37%, and 55% lower and the wear-resistance was 1500X, 30X, and 120X higher than those of pure Al, cast Al 319 alloy, and conventional Al2 O3 -Al composites, respectively. Wear scar examination showed severe adhesive wear on the conventional Al alloy and micro-composite surfaces; however, only mild abrasive wear was observed on the nanocomposite surfaces. It was observed that the particle concentration had to exceed a critical level (10–15 vol%) to exhibit superior wear-resistance, even though a lower level (e.g. 5 vol%) resulted in a significantly improved tensile strength.

A review was conducted of past laboratory-scale test methods and to assess their validity for ranking materials and lubricants for use as piston and liner materials in compression-ignition (CI) and spark-ignition (SI) engines. Most of the previous work was aimed at simulating SI engine environments. This report begins with a discussion of the numerous factors that can affect the validity of an approach to simulating engine conditions in a laboratory. These include not only mechanical, chemical and thermal factors, but also human factors as regards how the vehicle is operated and maintained. The next section provides an annotated review of open literature publications that address the issues of laboratory simulation of engine components. A comparison of these studies indicates a lack of sufficient standardization in procedures to enable a systematic comparison of one publication to another. There were just a few studies that compared several laboratory test methods to engine test results, and these indicated that some test methods correlate, at least qualitatively, better than others. The last section provides a series of recommendations for improving the accuracy and validity of laboratory-scale simulations of engine behavior. It became clear that much of the engine wear damage occurs during start-up whenmore » the engine is cold, and this calls into the question the usefulness of test methods that attempt to simulate steady-state running conditions. It is recommended that a new standard test method, perhaps developed with the help of the ASTM wear and erosion committee, be developed. It would use cold start-up conditions in the presence of degraded oil, or simulated degraded oil. « less

Nanocrystallinetitanium nitride films with very low carbon and oxygen content were deposited on single‐crystal silicon substrates from the reaction of tetrakis (dimethylamino) titanium, Ti[(CH3)2N]4, with ammonia at 633 K and a pressure of 665 Pa. The film consisted of ∼10 nm grains. The hardness of the film, measured by nanoindentation, was 12.7±0.6 GPa. The average kinetic friction coefficient, against type 440C stainless steel, was determined using a friction microprobe to be 0.43.