Thermal Plasma-Induced Surface Structuring of Mg-Alloy for Improvement of Mechanical Properties
摘要
Mg-alloy AZ91 is extensively used in medical applications due to its excellent biocompatibility and biodegradability. However, the low mechanical properties and corrosion resistance limit its uses in medical field. In present research work, the thermal plasma irradiation effects for various exposure times ranging from 5 to 25 min on surface morphology, structural, mechanical properties and corrosion rate of AZ91 have been investigated. Optical and SEM analyses show the growth of craters, pores, cavities, bumps and particulates structures on surface of exposed samples, whose density and size increase with increasing exposure time. The growth of these structures is attributed to plasma-induced sputtering, surface tension gradients and localized mass evaporation. The microhardness, yield stress and UTS along with dislocation line density initially decrease from 80 to 72 HV, 445-441 MPa, 488-480 MPa and 30 × 1014 m−2 to 7 × 1014 m−2 with increasing exposure time from 5 to 15 min and then increase up to 94 HV, 464 MPa, 520 MPa and 16 × 1014 m−2, respectively, with further increasing exposure time up to 25 min, which are well correlated with the initially decreasing and then increasing trend of crystallite size. The minimum corrosion rate is observed after the 10-min exposure time. The variation in mechanical properties and corrosion rate is attributed to variation in the density and size of β-phase Mg17Al12 particles as function of exposure time. Our finding is that at lower exposure times AZ91 exhibits the more ductile behavior (softening), whereas at higher exposure times it shows the less ductile behavior with enhanced hardness which makes it more suitable for the medical applications, auto industry and aerospace applications.