Permanent orthopedic implants made from titanium, stainless steel, or cobalt-chromium alloys cause stress shielding and lead to secondary surgery. Biodegradable magnesium-calcium (MgCa) alloys have the potential to minimize stress shielding as well as eliminate the need for secondary surgery. The critical technical challenge is that magnesium degrades rapidly in the human body. In order to slow the corrosion rate, surface treatments such as laser shock peening (LSP), shot peening, or burnishing have been reported in literature. Each of these surface treatments uniquely alters the surface integrity and consequent fatigue life. Even though surface treatments may be effective at slowing corrosion rates, it is important to ensure that they do not shorten fatigue life. The purpose of this study was to (1) develop a laser shock peening (LSP) surface treatment of a curved surface that adjusts the surface integrity of a MgCa alloy by varying the peening overlap ratio and (2) determine the effect of LSP on the fatigue life. Surface integrity was characterized by topography, microstructure, and microhardness. Fatigue life of laser peened and unpeened samples were measured by rotating bending fatigue tests. It was found that LSP increased the fatigue life of the peened MgCa samples. Implementing LSP at high overlap ratios reduced the surface pileup which resulted in a higher fatigue life. The fractured surfaces of the peened samples exhibited striation patterns which were more pronounced at higher peening overlap ratios.
Surface micro dents may act as lubricant reservoirs to reduce friction and wear in sliding and rolling contact applications. Surface patterning has become a valuable technique for fabricating micro dents. Alternative methods such as micromachining present obvious limitations in comparison with laser shock peening (LSP). In this paper, the use of LSP along with an automatic X-Y table proves to be an attractive and reliable method for producing micro dent arrays with enhanced surface integrity and free of cracks. Surface topography, residual stress, and microhardness of the fabricated micro dent arrays on polished Ti-6A1-4V have been characterized. It has shown that LSP is capable of efficiently fabricating mass micro dent arrays with controllable size. The center area of the peened dents has highest hardness. In addition, high compressive residual stress can also be created.
This paper investigated the effect of magnetic pulse welding (MPW) condition (welding power, surface scratches, and contamination) on the establishment of welding between aluminum and copper tubes, and the associated welding mechanisms. The results showed that higher applied power and surface scratches in tangential direction were in favor for good weld, and oil on the surface prevented welding. Direct evidences were obtained on local interface melting under a high welding power. CuAl intermetallics with different atomic ratios were identified by energy dispersion spectrum (EDS) chemical analysis and by microscratching test. The mechanisms of MPW and the process improvement were discussed.
Surface micro dents may act as lubricant reservoirs to reduce friction and wear in sliding and rolling contact applications. Surface patterning has become a valuable technique for fabricating micro dents. Alternative methods such as micromachining present obvious limitations in comparison with laser shock peening (LSP). In this paper, the use of LSP along with an automatic X-Y table proves to be an attractive and reliable method for producing micro dent arrays with enhanced surface integrity and free of cracks. Surface topography, residual stress, and microhardness of the fabricated micro dent arrays on polished Ti-6Al-4V have been characterized. It was found that a 10% density of micro dent array reduces coefficient of friction compared with a smooth surface. However, a higher dent density not necessarily reduces coefficient of friction.
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