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Monday, May 21, 2012: 11:40 AM
Room 335 AB (Hilton Americas Houston )
A summary of the research on the influence of thermal spray technologies on the high-cycle fatigue properties of specimens is presented. Bio-grade titanium powder (10-44um) was deposited onto grit blasted Ti6Al4V substrates using plasma and cold spray technologies. Non-treated specimens (reference set) as well as the grit blasted and the coated specimens were subjected to cantilever-beam cyclical bend loading with a constant deflection of the free end and the crack propagation in the specimens critical area was monitored via a drop in the natural resonance frequency. The number of cycles at 50% sample cross-section damage (fatigue life) was used as a criterion.
It was found that the grit blasting procedure significantly altered the resistance of the Ti6Al4V material to a micro-crack initiation and propagation: as compared to the reference set (fatigue life of 462 949 cycles), the grit blasting procedure increased the fatigue life by 81% (838 966 cycles). The thermal spray technologies exhibited an adverse effect: the plasma spray deposition of the Ti layer induced a drop in the average fatigue life to 65% of the grit-blasted set lives and the cold sprayed specimens exhibited the lowest average fatigue lives among the samples, 421 772 cycles, representing only 91% of the reference set lives. Based on the analyses of the internal stresses, FEM modeling, SEM analyses of the micro-structure and influence of the coating deposition on the substrate surface, two explanations of the adverse effect of coatings deposition are presented.
Based on the resonance frequencies of the tested bodies and the FEM modeling of the system, a novel concept of calculation of elastic moduli of the coatings is presented. Using the method, the moduli of plasma and cold sprayed Ti coatings were calculated as 7.2 GPa and 36.7 GPa, respectively (6.2% and 31.6% of bulk titanium)
It was found that the grit blasting procedure significantly altered the resistance of the Ti6Al4V material to a micro-crack initiation and propagation: as compared to the reference set (fatigue life of 462 949 cycles), the grit blasting procedure increased the fatigue life by 81% (838 966 cycles). The thermal spray technologies exhibited an adverse effect: the plasma spray deposition of the Ti layer induced a drop in the average fatigue life to 65% of the grit-blasted set lives and the cold sprayed specimens exhibited the lowest average fatigue lives among the samples, 421 772 cycles, representing only 91% of the reference set lives. Based on the analyses of the internal stresses, FEM modeling, SEM analyses of the micro-structure and influence of the coating deposition on the substrate surface, two explanations of the adverse effect of coatings deposition are presented.
Based on the resonance frequencies of the tested bodies and the FEM modeling of the system, a novel concept of calculation of elastic moduli of the coatings is presented. Using the method, the moduli of plasma and cold sprayed Ti coatings were calculated as 7.2 GPa and 36.7 GPa, respectively (6.2% and 31.6% of bulk titanium)