Effect of Post Heat Treatment on the Microstructure and Microhardness of Friction Stir Processed NiAl Bronze (NAB) Alloy
NiAl bronze (NAB) alloy is prepared by using friction stir processing (FSP) technique at a tool rotation rate of 1200 rpm and a traverse speed of 150 mm/min. A post heat treatment is performed at the temperature of 675 °C. The effect of heat treatment on the microstructure and microhardness is studied. The results show that the microstructure of the FSP NAB alloy consists of high density dislocations, retained β phase (β′ phase) and recrystallized grains. When annealed at 675 °C, discontinuous static recrystallization (DSRX) takes place. The content of β′ phase gradually decreases and fine κ phase is precipitated. After annealing for 2 h, both the microhardness of the FSP sample in the stir zone (SZ) and the difference in hardness between the SZ and base metal decrease due to the reduction of the dislocation density and β′ phase, accompanying recrystallized grain coarsening. With further increasing of the annealing time to 4 h, the aforementioned difference in hardness nearly disappears.
Residual stress and microstructure evolution of shot peened Ni-Al bronze at elevated temperatures
Abstract In this work, the relaxation of residual stress and strain hardening effect along with the evolution of microstructure of Ni-Al bronze at elevated temperatures were investigated. The samples were peened and then isothermal annealed at temperatures ranging from 200 to 400 °C for different time. The residual stress in the surface layer were determined by X-ray stress analyzer. Variations of domain size and micro-strain were estimated by X-ray line profile analysis in which the modified Williamson-Hall method with uniform deformation energy density model was employed. Experimental results showed that both residual stress and strain hardening effect relaxed dramatically in the initial stages and then gradually reached steady state. Although partially recrystallization occurred at higher temperatures, only part of compressive residual stress relaxed at each fixed temperature. The micro-strain and the dislocation density also declined with the heating temperature and exposure time increasing, which were presumably related to the vacancy transportation and dislocation rearrangement. Meanwhile, as demonstrated by XRD and TEM, the domain size increased significantly. The thermal relaxation activation enthalpies of residual stress and X-ray full width at half maximum were evaluated via Zener-Wert-Avrami relationship. The latter value was larger than that of residual stress, which indicated that the strain hardening effect was more difficult to fade at elevated temperatures. Hardness also reduced continuously during annealing process, which was mainly ascribed to the increased domain size and the weakening strain hardening effect. No phase transition occurred and the crystallinity was improved after annealing treatment. In the present study, the residual stress did not release completely even after annealing at the highest aging temperature for 2 h, which meant that shot peening could enable Ni-Al bronze alloys to keep excellent thermal stability of beneficial compressive residual stress.
On the ontology of particle mass and energy in special relativity
Einstein claimed that the fundamental dynamical insight of special relativity was the equivalence of mass and energy. I disagree. Not only are mass and energy not equivalent (whatever exactly that means) but talk of such equivalence obscures the real dynamical insight of special relativity, which concerns the nature of 4-forces and interactions more generally. In this paper I present and defend a new ontology of special relativistic particle dynamics that makes this insight perspicuous and I explain how alleged cases of mass–energy conversion can be accommodated within that ontology.