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A systematic study of the microstructure/fracture toughness/processing correlation of metal-ceramic composites in the Ti-B-Cu porosity system is presented. The composites are produced by the combustion synthesis process. Fracture surfaces indicate both ductile and brittle regions. The composites are made up of Ti as the only ductile phase and TiB, TiB2, Ti2Cu, and Ti3Cu4 as brittle phases. Density measurements and scanning electron microscopy (SEM) indicate that the samples contain distributed porosity. Ductile phase toughening is responsible for the increase in fracture toughness to a maximum value of 9.9 MPa(m)1/2. Samples with large amounts of porosity do not benefit from this toughening process even though they containin situ formed whiskers. The fracture toughness of the composite is modeled by considering the additive influence of the ductile phase reinforcement (Ashby model) and the residual porosity (exponential model). Microstructural constants required for the model are evaluated from the comparison. A correlation between the mechanical properties and the combustion temperature is established.

One of the major problems in the fabrication of aluminum-ceramic composites is the wettability of ceramic reinforcements by liquid aluminum. In this article, the wettability at the liquid metal/ ceramic particulates interface has been evaluated by means of an infiltration technique that permits a determination of the threshold pressure and the infiltration kinetics. The aim of the present article is to check the reliability of the experimental technique. The work was carried out on pure aluminum and A12O3, SiC, and TiC particulates of average diametersD in the range 7.5 to 150 μm. An Al-1 wt pct Pb alloy was also used to investigate the effects of surface tension. All infiltrations were carried out in air. The results for the infiltrated heightvs applied pressure or time follow Darcy’s law. On the other hand, threshold pressures are proportional to 1/D (capillary law) and some deviations can be ascribed to differences in the shape of the particulates (especially TiC). More than 75 pct of the reduction in the threshold pressure promoted by 1 wt pct of lead can be related to the decrease in the surface tension of pure Al. The results indicate that effects due to changes in wetting should be very small, as expected when aluminum is covered with an oxide layer.

Simple analytical expressions have been derived to express the activity of the solute in binary dilute solutions in terms of the Associated Solution Model (ASM) parameters. The activity coefficient of the solute at infinite dilution and the first and second order Wagner’s self-interaction parameters are, then, given as a function of ASM parameters for some simple cases.

The effect of hydrogen on the mechanical properties of the metastable β alloy Ti-10V-2Fe-3Al was examined. The material was beta annealed and water quenched (B/WQ) to yield a nominally all-β microstructure, with a small volume fraction of athermal omega present. Tensile and notched bend bar tests were performed with differing levels of hydrogen concentration (~0 to >30 at. pct) obtained by Sieverts (gaseous) charging prior to beta annealing. The β phase was transformed to orthorhombic alpha double prime martensite (β") upon deformation. The volume fraction and morphology of the alpha double prime depended on the hydrogen concentration. The deformation-induced martensitic transformation changed from being stress-induced to being strain-induced with increased hydrogen concentration. High hydrogen concentrations also resulted in changes in fracture mode. At high hydrogen concentrations, where little or no martensite formed upon deformation, “intrinsic” (i.e., independent of microstructural modification) hydrogen effects were observed in the β phase. These intrinsic hydrogen effects, deleterious in nature, were taken to be evidence of hydrogen embrittlement in the body-centered cubic β phase.

A series of 13 Fe-Cr-C alloys was studied to determine the phases present after the alloys were equilibrated for 1000 h at 870°C (1600°F). The alloys had a nominal composition of 1 pct carbon and 0 to 29 pct chromium. The experimental program employed: a) selective etching plus X-ray diffraction studies of extracted carbides to identify the carbides, b) quantitative metallography plus electrolytic carbide extraction to determine the quantity of carbides, and c) electron microprobe analyses plus chemical analyses of extracted carbides to determine the carbide compositions. Microprobe traverses through the carbide particles and the adjoining matrices showed that equilibrium had been established. The In and In6 carbides were all stoichiometric with respect to car bon—in contrast to most prior diagrams which show the M3C and M7C3 forming a pseudobinary system.