Calcium phosphate (CaP)-titanium (Ti) composites were processed using a commercial laser engineered net shaping (LENS™) machine to increase wear resistance of articulating surfaces of load-bearing implants. Such composites could be used to cover the surface of titanium implants and potentially increase the lifetime of a joint replacement. It was hypothesized that adding calcium phosphate to commercially pure titanium (CP-Ti) and Ti6Al4V alloy via laser processing would decrease the material loss when subjected to wear. This added protection would be due to the in situ formation of a CaP tribofilm. Different amounts of CaP were mixed by weight with pure Ti and Ti6Al4V powders. The mixed powders were then made into cylindrical samples using a commercial LENS™-750 system. Microstructures were observed and it was found the CaP had integrated into the titanium metal matrix. Compression test revealed that CaP significantly increased the 0.2% offset yield strength as well as the ultimate compressive strength of CP-Ti. It was found that the addition of CaP to pure titanium reduced the material loss and increased wear resistance. This was due to the formation of CaP tribofilm on the articulating surface. The in situ formed tribofilm also lowered the coefficient of friction and acted as a solid lubricant between the two interacting metal surfaces. Overall, CaP addition to Ti and its alloy Ti6Al4V show an effective way to minimize wear induced damage due to the formation of in situ tribofilm at the articulating surface, a strategy that can be utilized in various biomedical devices.
In this study, niobium carbidestainless steel 304 (SS304) metal matrix composite was processed using laser engineering net shaping (LENS). By laser bonding NbC particles with SS304, the NbC dispersed at the grain boundaries and in the lattice. XRD results showed that NbC addition caused lattice strain, which resulted in the strengthening of the matrix metal, increase hardness, and a >75% decrease in wear rate. The carbides became abrasive particles in the metal during wear, which increased the wear resistance along with the coefficient of friction (COF). Such coating approach via LENS™ could be utilized in specific locations to protect existing steel parts or be added to new ones that may be sensitive to wear degradation as opposed to treating the entire part surface.
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