Influence of polishing on cast clasp properties.
During the polishing of clasps, two possible changes that could affect their properties are thinning of the clasp and work hardening of the alloy. Two distinctly different clasp pattern forms were selected and 20 samples of each were cast. They were then divided into two groups, polished and unpolished, in an effort to determine the total influence of the polishing procedure on clasp behavior. The results indicate that polishing produces a slightly more flexible clasp. Any influence resulting from possible work hardening is offset by the reduction of clasp thickness. Effects of width/thickness ratios and magnitude of deflections on finishing and polishing techniques may also alter clasp flexibility in the polished clasp.
Stress-relaxation testing. Part II: comparison of bending profiles, microstructures, microhardnesses, and surface characteristics of several wrought wires.
1 h d 1 l’t t e enta I era ure fails to provide the profession with a thorough understanding of the wrought wires used as clasp materials in dentistry. All information currently available has largely been obtained through the use of tensile testing. In tensile testing, the atoms within the alloy are subjected to tensile stresses at a constant rate of loading. This is not representative of the type of stress present in clasp arms during clinical use. Since clasp arms are required to undergo repeated bending, both tensile and compressive stresses are developed within the material. The extent and rate of any clasp deflection vary. To provide data which can be analyzed to obtain results which can be applied to clinical situations, it is imperative that the test methods approach the conditions present during clinical function as much as possible. During stress-relaxation testing, the test specimen is deflected by the instrument and released. The resiliency of the material returns the test specimen to its original position in the same manner as a clasp arm, after it has passed beyond the curvature of the tooth. As the clasp is deflected, both the tensile and compressive stresses
Evolution of carbide precipitates in Hastelloy N joints during welding and post weld heat treatment
Abstract The effects of welding and post weld heat treatment (PWHT) on the morphology, composition and lattice parameter of the precipitates in the welding joints of Hastelloy N alloy have been investigated. Joint samples were prepared using a gas tungsten arc welding process with ERNiMo-2 fillers, and then solid-solution treated at 1100 °C for 20 min. After welding, eutectic M6C carbides can be observed in the heat affected zones (HAZ) and weld zones (WZ). These eutectic M6C carbides become spheroidized during the following PWHT. The concentration of Si decreases during the transformation from the primary ones to eutectic ones, and then increases during the spheroidizing process. The total concentration of Si + Cr in M6C carbides remains stable during welding and PWHT. At the same time, the heat leads to the outward diffusion of Mo from the M6C carbides, which results in a decrease of the lattice parameter.