In-situ Micro Mechanical Behavior Study Of Porous W/Zr-based Metallic Glass Composite

This paper takes as-cast and as-extruded porous W/Zr-based metallic glass compositesto be the object. The research focus on the values and distributions of the thermal residualstresses of the composites during the fabrication, as well as the stress evolution, the loadtransfer and the stress distribution in the two phases during quasi-static compression,using the high energy X-ray diffraction based on synchrotron radiation and finite elementmodeling. The main research results are as follows:The thermal residual stresses of the as-cast composites with the W volume fractions of67%,72%, and80%were calculated. The thermal residual stresses were compressive inthe W phase, and they were tensile in the metallic glass phase in all the principaldirections. The values of the thermal residual stresses decreased with the increasing Wvolume fraction, while the thermal residual stresses increased in the metallic glass phase.Compared with the as-cast composite, the residual stresses in the W phase of theas-extruded composite decreased slightly, indicating that the residual stresses caused byhydrostatic extrusion could be ignored.In the quasi-static compression test at room temperature, the W phase was the majorstress sustained phase in the early stage of deformation because of elastic strain misfitbetween the two phases. When the applied stress increased, the W phase yielded first,subsequently, the metallic glass phase became the major stress sustained phase. The yieldstrength of the metallic glass phase was higher than that of the composite. In the cycliccompression test, the yield strength of the W phase decreased with the increasing Wvolume fraction, while the extent of work hardening was increasingly significant with theincreasing W volume fraction. This phenomenon was due to the restriction of the metallicglass phase with elastic deformation to the motion of the dislocations in the W phase,however, when the metallic glass phase yielded, the dislocation tended to propagate awayfrom the interfaces and tangled in the inner W phase, showing the weak restriction ofinterfaces to the propagation of the dislocations. Yield stress of the tungsten phasedecreased with increasing tungsten volume fraction, which was influenced by the elastic strain mismatch between the two phases. The stress distribution difference between thetwo phases as well as the difference of the volume fractions between the two phasescaused yield strength of the metallic glass phase to decrease with increasing tungstenvolume fraction. The higher the W volume fraction was, the more well-distributed thedeformation of the as-cast composite was. The stress concentration led the two phases toseparate easily in the interphases. When the W volume fraction increased, the separationof the interphases was easier to occur.In the cyclic compression at different temperatures, the work hardening exponent ofthe W phase was almost the same at all the testing temperatures with the increasingloading numbers, which was attributed to the greater influence of the pre-deformationthan the influence of the softening of the metallic glass phase on the extent of workhardening in the W phase. The yield strength of the metallic glass phase decreased withthe increasing temperature. The yield strength of the metallic glass phase increased withthe increasing loading numbers at high testing temperatures, showing the “workhardening” phenomenon, which was because of the crystallization of the metallic glassphase when the testing temperature was higher than423K.In the quasi-static compression test at room temperature, the process of stresssustaining between the two phases in the as-extruded composite was similar to the as-castcomposite, but the yield strength of the metallic glass phase was lower than that of thecomposite. The grain orientation dependent stress in the W phase was slight because Wwas an isotropy material. In the three cyclic compression test, the yield strength of the Wphase, as well as the extent of work hardening of the W phase increased with theincreasing pre-deformation, because the process of hydrostatic extrusion could cause thework hardening in the W phase. The heterogeneity in stress was getting weaker with theincreasing pre-deformation, and the stress concentration was slight at the interphases, sothe interphase separation was hard to occur.