Roughening of metallic biomaterials by abrasiveless waterjet peening: Characterization and viability

This study addresses the roughening of AISI 316 LVM and Ti6Al4V by waterjet peening (WJP) without abrasive particles, looking for rough surfaces free of embedded particles that could act as severe notches. Strong parameters have been selected to characterize and check viability of abrasiveless WJP; a water pressure of 360 MPa and two slow traverse velocities: 0.05 and 0.1 m/min. After processing, large number of pits with undercuts plus some larger intrusions are observed, which are more abundant and larger in the steel specimens and in those treated with the lower traverse speed. Cross sectional examination of 316 LVM reveals a significant grain size refinement in the subsurface zone, 10–20 μm wide, that exhibits a submicrometric/nanometric grain size, accompanied with a hardness gradient (50% increase) that extends to a depth of up to about 100 μm. The analysis of the magnetic hysteresis loops discards the presence of strain induced α-martensite. No hardness or microstructural gradient was developed in the Ti6Al4V alloy. The results indicate that in AISI 316 LVM the volume loss occurs through hardening of the subsurface, embrittlement, crack formation and erosion. In Ti6Al4V the material removal may take place first at the vanadium reach β-phase.