Mechanical property and fracture behavior of squeeze-cast Mg matrix composites

Abstract

The present study aims to investigate the microstructure and fracture properties of AZ91 Mg matrix composites fabricated by the squeeze-casting technique, with variations in the reinforcement material and applied pressure. Microstructural and fractographic observations, along with in situ fracture tests, were conducted on three different Mg matrix composites to identify the microfracture process. Two of them are reinforced with two different short fibers and the other is a whisker-reinforced composite. From the in situ fracture observation of Kaowool-reinforced composites, the effect of the applied pressure on mechanical properties is explained using a competing mechanism: the detrimental effects of fiber breakage act to impair the beneficial effects of the grain refinement and improved densification as the applied pressure increases. On the other hand, for the composites reinforced with Saffil short fibers, microcracks were initiated mainly at the fiber/matrix interfaces at considerably higher stress intensity factor levels, while the degradation of fibers was not observed even in the case of the highest applied pressure. This finding indicates that the higher applied pressure yields better mechanical properties, attributable to the Saffil short fibers having relatively high resistance to cracking. Although an improved microstructure was obtained by accommodating the appropriate applied pressure in the short fiber-reinforced composites, their mechanical properties were far below those of conventional Al matrix composites. In this regard, the Alborex aluminum borate whisker is suggested as a replacement for the short fibers used in the present investigation, to achieve better mechanical properties and fracture toughness.

Effects of Tempering on Microstructure, Hardness, Wear Resistance, and Fracture Toughness of Cr3C2/Steel Surface Composites Fabricated by High-Energy Electron-Beam Irradiation

“…This test has shortcomings, such as introduction of a sharp notch instead of a fatigued precrack and thin specimen thickness, which does not satisfy the plane strain condition. It was reported that the toughness measured under the plane strain condition was similar to that measured under the plane stress condition for brittle materials, [20] and that the apparent fracture toughness obtained from the sharp-notch-inserted CT specimen was similar to that of the fatigued-crackinserted specimen. [21] Thus, the apparent fracture toughness of the surface composites could be evaluated reliably and comparatively.…”

“…In brittle materials such as surface composites, however, the fracture toughness measured under the plane stress condition does not deviate much from that measured under the plane strain condition. [20] Thus, the apparent values measured from this method can be used to evaluate the fracture toughness reliably on the comparative basis.…”

Practical Applicability and Limitation of Representative Volume Element Approach to Model Creep Behaviors of Metal Matrix Composites

“…In general, two different methods have been extensively used. The first basically included the Eshelby or "mean stress" theory, 6) which treats the strengthening of composites reinforced with elastic ellipsoidal inclusions.…”

Analysis of 3D Random Al<SUB>18</SUB>B<SUB>4</SUB>O<SUB>33</SUB> Whisker Reinforced Mg Composite Using FEM and Random Sequential Adsorption

“…[1][2][3] In order to facilitate the development and design of whisker reinforced composites, constitutive relationships must be developed that predict their effective elastic modulus and overall stressstrain response. Although some analytical and semi analytical models have been developed to evaluate the effective material properties of fiber and particle reinforced composites based on homogenization techniques, [4][5][6] they have not been able to be extended to composites with irregular reinforcement geometries and complex microstructures.…”