Assessment of blasting induced effects on medical 316 LVM stainless steel by contacting and non-contacting thermoelectric power techniques

Abstract

Grit blasting is a low cost surface modification treatment widely used to enhance mechanical fixation of implants through increasing their roughness. As a result of the severe surface plastic deformation, beneath the surface it produces additional effects such as grain size refinement, work hardening and compressive residual stresses, which are generally evaluated with destructive techniques. In this research work, the blasting induced effects by Al 2 O 3 and ZrO 2 particles and their evolution after annealing at 700ºC were evaluated in 316LVM (Low Vacuum Melting) stainless steel specimens using two non-destructive thermoelectric techniques (NDTT), the non-contacting and contacting thermoelectric power measurements. Microstructural analysis and microhardness measurements performed beneath the blasted surface reveals that the non-contact NDTT results correlate well with the reversion of the α'-martensite developed during blasting, whereas the contact NDTT results are closely related to the grain size refinement and work hardening and the expected evolution of compressive residual stresses. Potential of these techniques to monitor subsurface changes in blasting processes and others severe surface plastic deformation techniques are clearly envisaged.

Improvement of the blasting induced effects on medical 316 LVM stainless steel by short-term thermal treatments

“…Due to the very short annealing, the compressive residual stresses developed during blasting, which will serve to retard fatigue-crack propagation, are only partially released, as determined for similar samples by non-contacting thermoelectric measurements [20]. It is worth mentioning that partial relaxation of the compressive residual stresses would be counterbalanced by the reversion of α′-martensite and the induced grain size refinement of the microstructure [26], which would play a beneficial role.…”

“…In this work thermal treatments of blasted steel will be performed at 700°C for 2 min and 1 h, which in addition to the reversion of martensite could provoke a partial and a full relaxation of the residual stresses, respectively [20].…”

“…The detrimental role of the longest exposure can be associated with the full release of the initial compressive residual stresses, [20]. The lower fatigue strength of the thermally treated steel blasted with alumina particles can be related to their lower thermal expansion coefficient with regard to that of the matrix where they reside.…”

Thermoelectric assessment of laser peening induced effects on a metallic biomaterial Ti6Al4V

“…Thermoelectric power (TEP) measurements have recently gained a growing attention for the characterization of metallurgical properties in steels and other alloys. These measurements are sensitive to changes in the electronic structure of the material resulting from various metallurgical and mechanical processes [9][10][11][12][13][14]. The contacting thermoelectric technique analysis consists of measuring potential differences in the micro-volt range, generated by a small temperature difference along the sample.…”

“…Recently experimental results reported by Carreon et al [9][10][11] indicate that the stress-dependence of the thermoelectric power in metals produces sufficient contrast to detect and quantitatively characterize regions under compressive residual stress based on their thermoelectric contrast with respect to the surrounding intact material. The goal of this research work is to use two non-destructive thermoelectric techniques (NDTT), the non-contacting and contacting thermoelectric power measurements to sense the subsurface changes induced by laser peening in a metallic biomedical Ti-6Al-4V alloy.…”