[en] Experimental data are presented on the structure and mechanical properties of a rapidly solidified Al-8.1 Fe-1.7 V-1.3 Si alloy, designated as alloy 8009, which has been developed to meet the property specifications defined for high-performance aircraft applications. The specifications include retention of mechanical properties after exposure times of 100 and 1000 hours at temperatures up to 589 K. The results reported here show that 8009 alloy exceeds these requirements due to the structural stability of the uniform dispersion of fine silicide particles developed in the rapidly solidified samples. 2 refs

[en] Recent studies have demonstrated that a large number of ordered intermetallics exhibit environmental embrittlement in air at ambient temperatures. The embrittlement involves the decomposition of water vapor at metal surface, resulting in the generation of atomic hydrogen that diffuses into the alloys and causes brittle intergranular fracture. The authors' recent studies have shown that Ll₂-ordered (Co, Fe)₃V alloys containing 25 at. % V exhibit the environmental embrittlement. For instance (Co₇₈Fe₂₂)₃V alloy showed a high ductility of 36% when tested in vacuum at room temperature, whereas the ductility decreased to 20 and 16% when tested in air and distilled water, respectively. In this paper, the study of environmental embrittlement in (Co,Fe)₃V is extended to include effects of alloy stoichiometry. Hypostroichiometric alloys containing less than 25 at.% V were prepared and tensile tested in various environments at room temperature. The results are compared with those from the stoichiometric (CO,Fe)₃V alloy and other Ll₂ intermetallics and discussed based on available models predicting the grain-boundary cohesive strength

[en] Ni3Al alloys with a low boron content (120 wt ppm) are shown to be susceptible to environmental embrittlement in the presence of water vapor. When the boron content is sufficiently low, hydrogen released from the reaction of water vapor with aluminum atoms can reduce the beneficial plastisizing effect of boron, leading to lower ductility and intergranular cracking. Of the environments studied, gaseous hydrogen is the most harmful for Ni3Al. 19 refs

[en] The effect of Ce on the stacking-fault energy of Ni-Cr alloys is presently ascertained by the weak-beam method; TEM characterization results are compared with published data. A trend is noted which opposes the direction of the observed decrease in creep rate, indicating that diffusional flow is primarily affected by the Ce despite the very low Ce concentrations in question (119 at. ppm). The trend nevertheless fits the observed creep-activation energy increase. A similar effect is obtained with 225 at. ppm additions of Y to Ni-22Cr, where Y reduces Cr and Ni tracer diffusivities. 15 refs

[en] It has been speculated that the beta transus temperature of alpha2-beta alloys will be a function of the alloy's oxygen content. An effort is presently made to ascertain the effect of a wide variety of oxygen contents on the beta transus temperature of the Ti-25Al-10Nb-1Mo alloy. The beta transus temperature is established to be a strong function of oxygen content in the 710-1000 wppm range; above 1000 wppm, transus temperature becomes only a weak function. The temperature of the B2/bcc order-disorder transition is also a function of oxygen content. 4 refs

[en] The thermodynamic behavior of the intermetallic compounds Ni3Nb and Ni6Nb7 is described in terms of sublattice models proposed by Hillert and Staffanson (1970) and Sundman and Agren (1981). The optimized parameters of the compounds and a phase diagram are calculated. The calculated homogeneity ranges of Ni3Nb at 1273 K and Ni6Nb7 at 1373 are in good agreement with the results obtained by Duerden et al. (1966). 16 refs

[en] TEM and electron diffraction are presently used to characterize the structural relationships between the ordered tetragonal (T) and ordered orthorhombic (O) phases of a rapidly solidified Ti-24Al-11Nb alloy. It is established that the transition from the T to the O phase is explainable in terms of a shape-deformation mechanism, and that the T/O interface (habit) plane approximates -2 2 3 sub T. Attention is given to the orientation relationships between the two phases. 7 refs

[en] Initial microstructural characterization results are presented for the microstructure and properties of gas-atomized Ti-Al-Si-Nb alloy powders intended for HIP consolidation. Attention is given to the effects of rapid solidification on phase distributions and compositions. Two alloy compositions are studied: a eutectic and a hypoeutectic. Characterizations are by XRD, EDXS, SEM, and TEM. A dendritic solidification structure is exhibited by both alloys, together with a dual-phase microstructure consisting of metastable ordered beta and (Ti,Nb)5(Si,Al)3. 11 refs

[en] Several Nb-Al alloys, including single-phase NbAl3 and the eutectic of Nb2Al and NbAl3, were prepared either by nonconsumable arc melting in Ar or by zone processing in He following initial induction melting and rod casting, and the effect of the solidification route on the microstructure and room-temperature mechanical properties of these alloys was investigated. Automated control procedures and melt conditions for directional solidification of NbAl3 and the Nb2Al/Nb3Al eutectic were developed; high purity and stoichiometry were obtained. The effects of ternary additions of Ti and Ni are described. 7 refs

[en] The paper concentrates on mechanical alloying (MA), a high-energy ball-milling technique, used for preparing powders of Al3Ti, Al3Zr, and Al3Hf. The synthesis of these alloys by MA is reported, and the formation of metastable phases, the thermal stability of these phases, and their lattice parameters are discussed. It is noted that the closeness of the lattice and structure parameters between Al and the Al3X intermetallic phases offers the possibility of coherent precipitates in the Al matrix, while the use of hexane during MA leads to the formation of fine uniformly dispersed carbide precipitates in the matrix. It is pointed out that this, in combination with the fine grain size of the matrix and intermetallic precipitates should lead to cumulative improvements in the properties of the alloys. 23 refs