Dependence Of Deformation Mechanisms Research Articles

Dependence of deformation mechanisms on micro-pores in the fourth-generation single crystal superalloy during out-of-phase thermal-mechanical fatigue

The high-temperature and long-term solution heat treatments of fourth-generation single crystal (SX) superalloys have sparked an increasing number of homogenization pores in the alloy. Out-of-phase (OP) thermal–mechanical fatigue (TMF) experiments were conducted to elucidate the effect of pores on the fatigue behaviors and deformation mechanisms. The results showed that the plastic deformation was mainly concentrated upon γ matrix in regions away from pores, more specifically, intrinsic stacking fault (ISF) and extrinsic stacking fault (ESF) as well as dislocation cross-slipping were detected. In areas near micro-pores, however, the γ/γ′-structure was subjected to severe twinning shearing. High-resolution observation illustrated that the amount of ESF and a/6 〈112〉 twinning dislocations had remarkably increased. Besides, the partial dislocations were more prone to move in different slipping systems at these regions with considerable stress concentration. These factors collectively enabled the formation of deformation twins from the edge of micro-pores. Moreover, the twinning nucleation could occur near both H-pores and S-pores, while the increasing pore size would enhance the nucleation and propagation of pore-induced twins by a large margin. These findings reported have provided important guidance for the future application of the fourth-generation SX superalloys.

Elevated Temperature Tensile Behavior of a Nb-Mo Microalloyed Medium Mn Alloy under Quasistatic Loads

The elevated temperature tensile behavior of a Nb-Mo microalloyed medium steel was investigated over the −50 to 150 °C temperature range. The ultimate tensile strength was significantly reduced with increasing deformation temperature, but both YS (yield strength) and EI (total elongation) values changed slightly. The best product of UTS (ultimate tensile strength) and EI (~59.5 GPa·%) can be achieved at the deformation temperature of 50 °C, implying an excellent combination of strength and ductility. Furthermore, the change in strain hardening rate as a function of deformation temperature was further explained by the following two aspects: the dependence of mechanical stability of retained austenite on deformation temperature as well as the dependence of deformation mechanism on deformation temperature. Theoretical models and experimental observations demonstrate that the dominant deformation mechanism of the present medium Mn steel changed from the single transformation-induced plasticity (TRIP) effect at −50 to 50 °C to the multiple TRIP + TWIP (twinning-induced plasticity) effect at 50–150 °C.

Effects of alloying addition on deformation mechanisms, microstructure, texture and mechanical properties in Fe-12Mn-0.5C austenitic steel

In the present investigation, the dependence of deformation mechanisms on quaternary alloying addition has been investigated for medium Mn austenitic steel. A steel with composition Fe-12Mn-0.5C-X (X: Ni and Al), a medium Mn austenite steel was deformed up to 60% by cold reduction to investigate the deformation mechanisms and texture evolution. Electron Back-scattered Diffraction (EBSD) and X-ray bulk texture measurement have been performed to study the deformation behaviour. Deformed microstructure with increasing strain was systematically analyzed with respect to the alloying addition. SFE of the alloy can be tailored by the addition of alloying elements. In the present investigation, SFE has been tailored by addition of Carbon, Aluminium and Nickel. The highest deformation twin fraction has been observed in Ni added sample and the lowest in the Al-added sample. Visco plastic self-consistent (VPSC) simulation has been performed to understand the contribution of slip and twin activity during deformation.

Dependence of deformation mechanisms on grain orientations and their changes calculated based on Sachs model in magnesium alloy AZ31

During deformation, the orientation of a grain influences not only the deformation mechanisms (slip or twinning) and the specific selection of activated slip or twinning systems for that grain, but also the kinetics of different types of transformation. Schmid factor analysis was applied to determine the orientation dependency of deformation mechanisms in magnesium alloys AZ31 in this work. The orientation changes after the operation of the specific deformation mechanisms were also calculated based on Sachs model. It was found that different deformation mechanisms proceeded differently according to theoretical predictions. Basal slip occurred when basal planes of grains were tilted toward ND around TD. Prismatic slip dominated when basal planes were approximately perpendicular to TD. Calculation results also indicated that the operating of pyramidal 〈a〉 slip can not be neglected. {10 \( \bar 1 \)2} twinning was favorable when basal planes were approximately normal to RD and {10 \( \bar 1 \)1} twinning was analyzed to be related to the grains with basal orientations. The operating of 〈a + c〉 slip could greatly suppress the activating of twinning by our Schmid factor analysis. Basal orientations with TD and RD scattering can favor basal slip and tension twinning, respectively, after the operation of compression twinning based on the Schmid factor calculations.

Temperature dependence of deformation mechanism in bonding zone of TLP joint of nickel base single crystal superalloy after tensile test

A nickel base single crystal superalloy was transient liquid phase (TLP) bonded using Ni–Cr–B amorphous foil at 1230°C for 4 h. Tensile tests of the TLP joint were carried out at different temperatures under constant strain rate. The microstructures and the deformation substructures in the bonding zone of the joint were investigated. The results show that the deformation mechanism of bonding zone depends on test temperature greatly. At low temperatures, the deformation is dominated by γ′ shearing; at high temperatures, the deformation occurs by means of γ′ bypass; at intermediate temperatures, the deformation exhibits a transitional behaviour. The deformation mechanism of different parts of TLP joint is identical.

Molecular orientation behaviour of uniaxially stretched poly(vinyl chloride) film: 2. The fourth moment of molecular orientation measured by the polarized fluorescence method

In order to measure the fourth moment of molecular orientation of poly(vinyl chloride) film a new polarized fluorescent method is examined. The fundamental principle of the method is to employ the polyene and the carbonyl radicals formed in the molecular chain, at the working process or with heat treatment, instead of a fluorescent dyestuff. It is necessary, in this method, to estimate the ratio of polyene to carbonyl in the sample, and the value is found to be 1.5 for unheat treated PVC film or 1.0 for heat treated PVC film. The second moment 〈cos 2ϑ〉 and the fourth moment 〈cos 4ϑ〉 are evaluated from the fluorescence intensity pattern. The applicability of this method is verified by comparison with the second moment derived from the birefringence. Dependence of deformation mechanism on draw temperature and plasticizer content are also investigated on the basis of a structural model composed of the characterized molecular chain, the practicability of which was already established by observations of the change in birefringence with draw ratio.