Dry friction and wear tests were performed on as-cast Mg97Zn1Y2 alloy using a pin-on-disc configuration. Coefficients of friction and wear rates were measured as a function of applied load at sliding speeds of 0.2, 0.8 and 3.0 m/s. The wear mechanisms were identified in the mild and severe wear regimes by means of morphological observation and composition analysis of worn surfaces using scanning electron microscope (SEM) and energy dispersive X-ray spectrometer (EDS). Analyses of microstructure and hardness changes in subsurfaces verified the microstructure transformation from the deformed to the dynamically recrystallized, and properties changed from the strain hardening to dynamic crystallization (DRX) softening before and after the mild–severe wear transition. The mild–severe wear transition can be determined by a proposed contact surface DRX temperature criterion, from which the critical DRX temperatures at different sliding speeds are calculated using DRX dynamics; hence transition loads can also be calculated using a transition load model. The calculated transition loads are in good agreement with the measured ones, demonstrating the validity and applicability of the contact surface DRX temperature criterion.
High-performance ceramic-lined composite steel pipes (CLCSPs) were fabricated by self-propagating high-temperature synthesis and centrifugal casting technique. ZrO 2 powders doped by 3 mol% Y 2 O 3 were added into Al-Fe 2 O 3 thermit to improve the mechanical properties of CLCSPs. The phase constituents and microstructural evolution of ceramic layers after addition of ZrO 2 were analyzed by means of X-ray diffractometer, optical microscope, scanning electron microscope and energy dispersive X-ray spectrometer. The effects of ZrO 2 on fracture toughness of ceramic layers, and crushing strength as well as mechanical shock of CLCSPs were investigated using Vickers indentation microfracture method, squeezing test and repetitive impacting method. The results show that addition of ZrO 2 changes the morphology and preferential orientation of Al 2 O 3 dendrites, and reduces the width of Al 2 O 3 dendrites, leading to the microstructure of Al 2 O 3 dendrites with ne t-ZrO 2 phase particles distributed at boundaries. The hardness of ceramic layer decreases, while the crushing strength of CLCSP changes slightly after addition of ZrO 2 . The fracture toughness of ceramic layer is signi cantly enhanced; meanwhile the mechanical shock resistance of CLCSPs was also greatly improved by adding more than 2% ZrO 2 . The optimum adding amount of ZrO 2 is
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