[Surface characterisation of shot peened implants with glas beads in total hip arthroplasty]

Fatigue performance of medical Ti6Al4V alloy after mechanical surface treatments

Mechanical surface treatments have a long history in traditional engineering disciplines, such as the automotive or aerospace industries. Today, they are widely applied to metal components to increase the mechanical performance of these. However, their application in the medical field is rather rare. The present study aims to compare the potential of relevant mechanical surface treatments on the high cycle fatigue (R = 0.1 for a maximum of 10 million cycles) performance of a Ti6Al4V standard alloy for orthopedic, spinal, dental and trauma surgical implants: shot peening, deep rolling, ultrasonic shot peening and laser shock peening. Hour-glass shaped Ti6Al4V specimens were treated and analyzed with regard to the material’s microstructure, microhardness, residual stress depth profiles and the mechanical behavior during fatigue testing. All treatments introduced substantial compressive residual stresses and exhibited considerable potential for increasing fatigue performance from 10% to 17.2% after laser shock peening compared to non-treated samples. It is assumed that final mechanical surface treatments may also increase fretting wear resistance in the modular connection of total hip and knee replacements.

Deep rolling of titanium rods for application in modular total hip arthroplasty

Compressive residual stresses are commonly introduced into the near-surface regions of morse taper junctions of modular hip endoprostheses to prolong fatigue life. An increasing number of publications report that contamination of shot-peened surfaces can lead to enhanced corrosion and third body wear. This study evaluates deep rolling of titanium alloy rods as a possible alternative to shot peening. Ten rods of Ti6Al7Nb alloy with a diameter of 15 mm were deep rolled with various rolling parameters. The resulting surface topography and residual contamination was analyzed using a scanning electron microscope (SEM). The near-surface residual stress states after deep rolling were characterized by means of X-ray diffraction. The roughness of the surfaces before deep rolling was about R(z) = 14 microm, and after deep rolling surface roughness values of R(z) 0.4-7.5 microm were achieved. The results of the SEM and EDAX analyses of the sample surface showed no evidence of surface contamination by particles or abrasion products caused by any process. At a pressure of 300 bar, compressive stress reached the maximum of -1150 MPa at a depth of 0.1 mm. Deep rolling thus allows a smooth and particle-free surface to be obtained and therefore shows promise as a surface treatment for mating surfaces of morse tapers in modular hip endoprostheses.