الفهرس 
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Abstract
This study investigates the effect of different heat treatment processes on dry sliding wear resistance of the TC21 titanium alloy at several levels of normal load and sliding speed. Response Surface Methodology (RSM) has been used as a design of experiment procedure. An experimental plan based on Central Composite Design (CCD) for the three input factors: heat treatment, load, and speed was carried out. The results revealed that under extreme conditions of load and speed for samples subjected to water quenching and aging (WQ + aging) _with highest hardness_ they possessed the poorest wear resistance. Samples left in annealed condition showed the highest wear resistance regardless they had much lower hardness. A mathematical polynomial model in a form of the inverse square root of wear resistance, Wr as a function of the input factors has been developed and validated successfully. The experimental values are within the 95% prediction interval of the model with an average absolute error of 3.91%. Based on the ANOVA outcomes, the normal load has been identified as the most significant input factor, followed by sliding speed and heat treatment. Besides, the interaction of load and speed was found to be significant. An optimization process to get minimum Wr under severe conditions has been achieved with maximum desirability of 0.665. Results were justified with help of FESEM (Field-Emission Scanning Electron Microscope) examination of the samples worn surfaces and XRD (X-Ray Diffraction) analysis of wear debris. The current study presents a novelty with respect to modeling and optimizing of dry sliding wear behavior of the TC21 titanium alloy.
Keywords: TC21, titanium alloy, heat treatment, wear rate, wear resistance, wear, tribology, DOE, RSM, ANOVA, CCD.