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NASA IIB-11, a candidate alloy for advanced temperature turbine engine disks, and four modifications with varying C and Hf concentrations were produced from prealloyed powders. Several notable effects of C and Hf concentration in the alloys were observed. Both the amount of the γ′ phase and its solvus temperature increased with decreasing C, but only the γ′ solvus was affected by Hf, increasing with increasing Hf. Hf also promoted a cellular γ′ precipitation. Hf was, however, about equally distributed between γ′ and γ. Hf and C both affected the carbides formed. Increasing both promoted formation of an MC relative to that of an M6C.

Transmission electron microscopy (TEM) was utilized to characterize the deformation substructure of 304 stainless steel tested for transgranular stress corrosion cracking (TGSCC) in 45 wt pet MgCl2 at 155 °C. The TEM characterization was conducted in thin foils prepared from the fracture surface and from a series of known depths below the fracture surface. The results indicate that the stacking fault energy (SFE) of the material immediately ahead of the crack tip is lowered, with the deformation mode at small distances (a few microns) in front of the growing crack front being entirely coplanar while at larger distances homogeneous. The reduction in the SFE is attributed to absorbed hydrogen formed during the cathodic reaction. Based on this and previous observations of transgranular stress corrosion characteristics of aus-tenitic stainless steels in chloride environments, a “hydrogen-induced cleavage” model is proposed. This model is essentially a modification of a model based on enhanced structural reactivity associated with Lomer-Cottrell locks proposed by Robertson and Tetelmann in 1962.27

The toughness behavior of high hardness laminar composite steel (high carbon, ∼ Rc 60, hard layer metallurgically bonded to a medium carbon ∼Rc 50, softer layer) was investigated. The effort focused on the effect of test temperature, specimen orientation and crack location on toughness. Charpy V-notch specimens with the notch extending through both the hard and soft layers were tested over a series of temperatures to provide transition curves for both the longitudinal and transverse direction. These transition curves are compared to those obtained from specimens that were surface notched on either the hard or soft side. By precracking similarly oriented specimens, information on the fracture toughness (K Q andW/A) was obtained over approximately the same temperature range. These data show the effect of the interface between the hard and soft layer on the various toughness parameters. Lastly, stress corrosion cracking was investigated andK ISCC values provided.

The changes in X-ray diffraction intensity and internal friction within and beyond the incubation period of bainitic transformation on the isothermal TTT diagram in a silver-cadmium (43.3 wt pct Cd) alloy were studied. Experimental results show that the parent-phase X-ray diffraction intensity and the internal friction value increase immediately at the beginning of isothermal holding and that the internal friction reaches its maximum value,Q −1 max within the incubation period. It then gradually decreases. It is suggested that the prebainitic transformation within the incubation period is the nucleation process of bainite.

Explosive densification following combustion synthesis of titanium and graphite powder mixtures has been used to fabricate bulk compacts (100-mm diameter × 20-mm thick) of TiC ceramics. A model rocket ignitor was used to initiate the combustion reaction in ≈65 pct dense green pressed reactants of titanium and carbon powder mixtures. Upon completion of reaction, the reacted mass was allowed to cool. After the desired time delay (t d) and while the reacted mass was still above the ductile-brittle transition temperature, an explosive charge was detonated in contact with a steel driver plate to transmit the pressure into the reacted mass and consolidate it to solid density. Temperature-time cooling profiles for the reacted material were developed using calculations based on a heat flow model. The explosive loading conditions, namely, the densification pressure controlled by the ratio of explosive charge mass (C) to driver plate mass (M) ratio (C/M) and thet d between the combustion reaction completion and explosive detonation, were observed to critically affect the density and the microstructure of the final compacted reaction product.

The phenomenological double-shear theory of martensite crystallography has been applied to the β → α′ martensitic transformation in the U-1.6 at. pct Ga alloy. A correspondence matrix for the β → α′ transformation was derived from the experimentally determined β/α′ orientation relationship, and the double lattice invariant shear was considered as a combination of the principal slip (010) [100]a with one of the minor slips in the α-uranium structure. The theoretical predictions of the habit plane are in good agreement with the experimental observations.

Adequate tensile and smooth stress rupture properties were achieved by heat treating p/m IN-792 to produce serrated grain boundaries pinned with a globular M23C6 precipitate. A notch-strengthened condition with Kt = 3.5 at 1400‡F (1033 K)/90 ksi (620 MN/m2) was achieved when the material was heat treated to produce a grain size larger than about 76 Μm (ASTM G.S. #6). To obtain this grain size using realistic solution time-temperature heat treatments, the carbon content of the IN-792 should be maintained below 0.1 pct and preferably about 0.04 pct.