| Abstrakt: |
The fractographic features of the fractures of W-Ni-Fe (90∶7∶3) powder composite material depend upon the character of fracture of the basic structural constituents. The refractory constituent may fracture in the grain boundaries (W-Ni, W-W) and transgranularly with the formation of a fan-shaped, river, or herringbone pattern. Fracture of the γ-solid solution may also be inter- and transgranular by brittle rupture without traces of plastic deformation (in the boundaries of the grain colonies and the basic structural constituents), by the formation and merging of voids, and by shear leading to pulling out "at the tooth" and failure of the cross-links (in the volume of the grain and in the boundary zones). The change in the forms of fracture, including at the boundaries of the basic structural constituents, in accordance with the conditions of the metallurgical process reflects the concurrent influence of segregation phenomena on the boundaries and of the processes of decomposition of the γ-solid solution on the geometry, degree of deformation, ratio of the properties, and mechanisms of fracture of the body of the grain and the boundary volumes in these constituents. The combination of different forms of fracture of the structural constituents in relation to the production prehistory influences the position of the ductile-to-brittle transition temperature range and, consequently, the properties of the alloy at a specified temperature. The alloy with increased strength and plasticity characteristics at room temperature is characterized by primarily transgranular fracture of the grains of the refractory constituent and of the γ-solid solution in which these grains are dispersed. Further investigations of the alloy must be directed to studying by transmission electron microscopy the fine crystalline structure of the basic constituents (nickel-base aging solid solutions and tungsten) and revealing the conditions of formation of the optimum structure of these constituents and the adhesion-strong boundaries providing occurrence of the effect of composition hardening. Obtaining the required level and stability of the properties of W-Ni-Fe alloy is related to establishment of the allowable interstitial element impurity content, revealing of the "dangerous" substitutional impurities, and optimization of the conditions of heating, cooling, and heat treatment providing a reduction in the influence of segregation phenomena in the boundary volumes on the geometry of deformation and on fracture. [ABSTRACT FROM AUTHOR] |
