Grindability of Ti alloys

Abstract

The grindability of Ti-based alloys was analyzed by considering the fracture behavior of individual alloys in response to the stress field of a grinding wheel. First, the stress field under a grinding wheel was computed by treating the grinding wheel as a cylindrical disk with a flat region acting on a flat substrate. The initiation and propagation of microcracks in the substrate was then examined on the basis of the contact stress field and one of two fracture criteria: (1) a critical stress criterion for the onset of cleavage crack initiation, and (2) a critical stress intensity factor criterion for the initiation and propagation of shear cracks. Grindability was computed as a function of grinding speed and microstructure for several Ti-based cast alloys containing ␣, ␣ ϩ ␤, or ␤ microstructure with or without the intermetallic precipitates. Model predictions indicated that the grindability of Ti alloys increases with decreasing fracture toughness or tensile ductility. The theoretical results are compared against experimental data in the literature to elucidate the roles of microstructure in grindability. The comparison revealed that alloying addition that leads to the formation of brittle intermetallics enhances grindability by reducing fracture toughness, tensile ductility, and the resistance to crack initiation and propagation.

Grindability of Dental Cast Ti-Zr Alloys

“…27,28) The elongation of Ti-Zr alloys became lower than that of titanium as the concentration of Zr increased. [11][12][13] The grinding rates of the Ti-Zr alloys increased at low speed as the concentration of Zr increased, in other words, as their elongation decreased, and the rates of the 30% Zr alloy were significantly higher than those of titanium.…”

Grindability of alpha-case formed on cast titanium

“…In our theoretical study of grindability for titanium alloys 30) , we found that their grindability increased with decreasing fracture toughness (KIC) and tensile ductility. What we found in the present study was that the grindability in the α-case layer was higher than the bulk material.…”

“…According to the grinding theory developed by Chan et al 30) the grinding rate, GR, for K-controlled fracture of Ti alloys is given by…”

“…Thus, several research groups have investigated the machinability/grindability [the relative ease of removing metal 21) ] of cast dental titanium 16,[22][23][24][25] . One of our research efforts has been concentrated on finding titanium alloys with improved grindability for the benefit of effective processing of titanium castings 18,[26][27][28][29][30][31] . The majority of our studies, just like investigations at other institutions, were performed for specimens whose α-case layer was totally removed.…”

“…These results suggested that grinding the α-case probably is not troublesome, contrary to earlier reports 15,16) . Based on our considerable experience in the evaluation of the grindability of titanium alloys, we theorized that the grindability of titanium alloys was enhanced 30) when titanium alloys have microstructures that increase brittleness, and reduce tensile ductility, fracture toughness, and the resistance to crack initiation and propagation. The α case usually has a Vicker's microhardness number ranging from 500 to 600 as compared to that of more ductile interior structures ranging from 200 to 300 33) .…”