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Oxide dispersion strengthened (ODS) nickel based alloys were developed via mechanical milling and spark plasma sintering (SPS) of Ni-20Cr powder with additional dispersion of 1.2 wt.% Y 2 O 3 powder. Furthermore, 5 wt.% Al 2 O 3 was added to Ni-20Cr-1.2Y 2 O 3 to provide composite strengthening in the ODS alloy. The effects of milling times, sintering temperature, and sintering dwell time were investigated on both mechanical properties and microstructural evolution. A high number of annealing twins was observed in the sintered microstructure for all the milling times.However, longer milling time contributed to improved hardness and narrower twin width in the consolidated alloys. Higher sintering temperature led to higher fraction of recrystallized grains, improved density and hardness. Adding 1.2 wt.% Y 2 O 3 to Ni-20Cr matrix significantly reduced the grain size due to dispersion strengthening effect of Y 2 O 3 particles in controlling the grain boundary mobility and recrystallization phenomena. The strengthening mechanisms at room temperature were quantified based on both experimental and analytical calculations with a good agreement. A high compression yield stress obtained at 800 °C for Ni-20Cr-1.2Y 2 O 3 -5Al 2 O 3 alloy was attributed to a combined effect of dispersion and composite strengthening.

The effect of friction stir processing (FSP) on mechanical and wear behavior was investigated for A-286 stainless steel, an Fe-Ni-Cr based austenitic, precipitation hardened alloy. The alloy was characterized in different processed conditions, namely as rolled (AR) + aged and FSP + aged. High frequency reciprocating sliding wear behavior and wear mechanisms were investigated at room temperature. The Vickers microhardness and wear rates were measured and compared for each processing condition. It was determined that along with increasing microhardness in the stir zone, FSP resulted in improved wear resistance. Specifically, the wear rate in the stir zone was reduced from 1 x 10-6 to 6 x 10-7 mm 3 /N•m due to FSP. Mechanistic studies were conducted to determine the effect of FSP on the microstructural evolution during wear. Scanning electron microscopy revealed increased coarse abrasion with the AR + aged alloy as compared to much finer-scale microabrasion with the FSP + aged alloy. This resulted in smaller and less abrasive wear debris, and hence lower wear rate. Furthermore, cross-sectional focused ion beam microscopy studies inside the stir zone of the FSP + aged alloy determined that increased microhardness was due to FSP-induced microscopic grain refinement resulting in Hall-Petch strengthening, and the corresponding wear rate decrease was due to even finer wearinduced grain refinement. With both effects combined, the level of surface fatigue wear was suppressed resulting in reduction of the wear rate. In contrast, the absence of FSP-induced grain

A steel/cemented carbide couple is selected to generate a tough/hard two layers material. The sintering temperature and composition are chosen according to phase equilibria data. The choice of optimal sintering conditions needs experimental studies. First results evidence liquid migration from the hard layer to the tough one, leading to porosity in the hard region. The study of microstructure evolution during sintering of the tough material (TEM, SEM, image analysis) evidences the coupled mechanisms of pore reduction and WC dissolution, and leads to temperature and time ranges suitable to limit liquid migration. The sintering of the two layer material is then shown to need further compromises to avoid interface crack formation due to differential densification.

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