Determination of residual stress within complex-shaped coarse-grained cobalt–chromium biomedical castings

Abstract

ASTM F75 femoral knee implant casting components distort during manufacture due to residual stress re-distribution or inducement. These castings pose a number of challenges for residual stress determination methods; they have a complex geometry, their microstructure is inhomogeneous, they work-harden rapidly and they have a coarse, elasticallyanisotropic grain structure. The contour method is anticipated to be the most promising residual stress determination technique. X-ray diffraction is feasible for components which have experienced plastic deformation on their surface which results in refined diffracting domains. Centre-hole drilling is feasible, but the influence of stress induced from drilling and the effect of coarse grain-structure is unknown. Neutron diffraction is challenging also due to a coarse grain structure and difficult nuclear material properties.

Application of multiple residual stress determination methods to coarse-grained biomedical implant castings

“…Given that cast ASTM F75 exhibits a coarse grain-structure and that FCC crystals directions will be dependent on the solidification direction during casting, texture may exist within the femoral [1]. Figure 8 and were calculated as follows:…”

“…Therefore, flowering is either the result of residual stress being induced or pre-existing residual stress redistributing [1]: Flowering results in femoral components which are not within specification and are thus either rejected or re-worked depending on each manufacturer's own processes. There is therefore the potential for significant improvements in the efficiency of the manufacturing process which would result in reduced business and environmental cost.…”

“…Ref. [1] was a literature review for the determination of residual stress within ASTM F75 femoral components with some initial experimental results reported for x-ray diffraction and the centre-hole drilling method. From Ref.…”

“…From Ref. [1] it was concluded that the determination of residual stress within as-cast ASTM F75 femoral implants would be challenging as they have a complex geometry, their micro-structure is inhomogeneous, they work-harden rapidly, they have poor neutron scattering properties and they have a coarse, elastically-anisotropic grain structure. Therefore, certain techniques would be limited in their application and would require various non-conventional experimental efforts.…”

X‐Ray Diffraction Technique for Residual Stress Measurement in NiCrMo Alloy Weld Metal

“…However, there are some difficulties in stress measuring both for neutron and X-ray diffraction methods in weld metals characterised with preferential orientated and coarse grain microstructure. In the case of nonferrous metals and its alloys, especially nickel alloys, such microstructure features can make difficult the analysis of XRD weld metal stress state [11,12].…”