Microabrasion-corrosion of cast CoCrMo alloy in simulated body fluids

Wear and corrosion of metal-on-metal hip replacements results in wear debris and metal-ion release in vivo, which may subsequently cause pain and hypersensitivity for patients. Retrieved metal-on-metal hip replacements have revealed that two-body sliding wear and three-body abrasive wear are the predominant wear mechanisms. However, there is a lack of understanding of the combined effects of wear/corrosion, especially the effect of abrasion-corrosion.

This study investigates the sliding-corrosion and abrasion-corrosion performance of a cast CoCrMo alloy in simulated hip joint environments using a microabrasion rig integrated with an electrochemical cell. Tests have been conducted in 0.9% NaCl, phosphate buffered saline solution, 25% and 50% bovine serum solutions with 0 or 1 g cm(-3) SiC at 37 degrees C. Experimental results reveal that under abrasion-corrosion test conditions, the presence of proteins increased the total specific wear rate. Conversely, electrochemical noise measurements indicated that the average anodic current levels were appreciably lower for the proteinaceous solutions when compared with the inorganic solutions. A severely deformed nanocrystalline layer was identified immediately below the worn surface for both proteinaceous and inorganic solutions. The layer is formed by a recrystallisation process and/or a strain-induced phase transformation that occurs during microabrasion-corrosion. (C) 2008 Elsevier Ltd. All rights reserved.

Aging Behavior of YAl2p/Mg-14Li-1Al Composite

YAl2p/Mg-14Li-1Al composite was made by a stir-casting technique. The aging behavior of the composite was investigated using hardness test, differential scanning calorimetry, and X-ray diffraction. The results show that the microhardness variations of both the matrix alloy and its composite are related to the precipitation and decomposition of θ-MgLi2Al phase. The strengthening of the composite is from the addition of YAl2 particulates and the precipitation in matrix alloy. The former contribution is stable, but the latter is unstable and depends on the aging behavior. The addition of YAl2 particulates delays occurring of the aging behavior of composite.