A comparison is made of microstructures of droplets of Ni-Sn alloys rapidly solidified (a) by gas atomization and (b) in a glass emulsifying medium. Cooling rate of the gas atomized particles ranged from 103 to 106K/s depending on droplet diameter (20-230μm). In the hypoeutectic alloy studied (Ni-25wt%Sn), most particles showed a dendritic structure. These same particles, melted and resolidified in a glass medium using DTA (Differential Thermal Analysis), showed undercoolings up to 280K: the structures were dendritic at low undercoolings and non-dendritic at undercoolings above about 220K. It is concluded that (1) the gas atomized particles exhibited little or no undercooling before nucleation, (2) the solidification time of the undercooled emulsified droplets is substantially less than that of gas atomized droplets, and (3) the undercooling required to achieve non-dendritic structure depends on sample size.

Laserglaze with appropriate post heat treatment has improved the thermal fatigue resistance of a wrought nickel-base superalloy. It was found that laserglaze was able to eliminate the blocky MC phase, refine grains and form a very interesting microstructure of serrated grain boundaries. Careful selection of post heat treatment markedly increased the strength in the laser irradiated region. The initiation and propagation of thermal fatigue cracks were suppressed by this novel microstructure.

The creep behavior of the fine grained, intermetallic superplastic alloy of overall composition Ni7 5 B1 7Si8 prepared by crystallizing an amorphous precursor was studied in the temperature range between 500 and 615°C, the stress range between 36 and 800 MPa, and for grain sizes between 6.8 and 1.12*10−5 mm. The strain rates measured varied between 10−7 and 6*10−5 sec−1.

Two different creep deformation mechanisms were observed. At low applied stresses, the material deformed in a diffusion controlled mode, with proportional to σ1. No dislocations developed in the grains, and the activation energy for creep was 4 eV. This value is higher than the self-diffusion of Ni in Ni (the principal constituent in the alloy) in agreement with observation in other Ni based alloy systems. At high applied stresses, a second mechanism became rate limiting. The activation energy of this process is about 0.6 eV and dislocations develop in the interior of grains when this mechanism operates.

The transition between the two regimes is grain size and temperature dependent and occurs at about 400 MPa at a deformation temperature of 550°C and a grain size of 6.8 10−5 mm. An analysis of the grain size dependence of creep strain rate as well as its absolute value indicates that the low stress regime is Coble type creep.

Studies of the elemental composition of carbide phases formed by rapid solidification of a Mo-base high speed steel (M7) have yielded an intriguing finding. Micro-analysis of the extracted carbides (M2C, M23C6 and MC) showea that these were unusually rich in refractory elements with values of Mo in the range 46-53 wt.%, corresponding values for Fe and Cr were low (6-12 wt.% Cr and 1.5-13 wt% Fe). This was in marked contrast with analyses of MC, M6C, M7C3 and M23C6 in the ‘unglazed’ material where Fe and Cr were major constituents. A distinctive feature was M23C6 in the rapidly solidified material which contained large amounts of Mo and W and very little Cr. It is proposed that this phase, initially formed as M6C, underwent solid-state transformation.

The surface melting of cast irons is discussed with particular emphasis on composition and effect of impurities. The hardness and wear properties are outstandingly good as shown from tracks under normal working conditions.

The microstructures of rapidly solidified Type 304 stainless steel powders produced by vacuum gas (VGA) and centrifugal atomization (CA) have been examined. The solidification morphology and phase distribution have been characterized using optical and scanning electron microscopy, and the relative amounts of ferrite and austenite have been quantified using x-ray diffraction. Most CA powder particles contain both fcc and bcc phases, with the bcc phase predominating at small particle sizes and the fcc phase at large particle sizes. The VGA powder generally contains less ferrite, with very little dependence on the particle size. The ferrite was metastable and transforms to austenite on annealing at 900°C.

High carbon content iron base alloys (2–4 wt%) with various alloying additions,eg., Cr, Ni, Si or Te were produced in powder form by water atomisation. Depending on the alloying addition the powder particles solidify, microcrystalline with either dendritic or cellular microstructures with supersaturated solid solution and eutectic. The proportion of carbide is dependent on the composition and atomizing conditions. The powder, after suitable preparation, was consolidated by extrusion or hot isostatic pressing. The consolidation behaviour of the powders is influenced by the composition and particle size distribution. The microstructures and hardness values of the powder in the as quenched state are compared with those of the consolidated state with particular emphasis on the thermal stability. The mechanical properties of extruded powders are compared with those for hot isostatically pressed.

Fracture processes have been studied in a fully crystallized Co84Nb10B6 glass, with the mean grain size ranging from 43 nm to 0.65 μm. Tensile tested specimens with a mean grain size≥ 0.3 μm showed a ductile (dimple) fracture with microvoids initiated at the boride-cobalt matrix interfaces. As the mean grain size (more correctly, the corresponding mean free path of the deforming cobalt phase) was ≤ 0.1 μm, the fracture process may be similarly initiated by the microvoid formation at the boride-cobalt interface. However, one-to-one correspondence between dimples and boride particles may not be preserved. As a result, dimples become more shallow and may include several boride particles instead. Although the fracture surface of the brittle fine grained Co84Nb10B6 alloy gives an appearance of a cleavage fracture on a macroscale, it is distinctly different, by allowing for the microvoid formation on a microscale.

Alloys of Cu-Sn and Cu-B have been processed by both melt spinning and ion implantation. In some instances (eg Cu-Sn alloys) rapidly solidified ribbons have been subjected to further implantation. This paper describes the similarities and differences in structure of materials subjected to a dynamic and contained process. For example in Cu-B alloys (up to 2wt% Boron) extended solubility is found in implanted alloys which is not present to the same degree in rapidly solidified alloys of the same composition. Likewise the range and nature of the reversible martensitic transformation is different in both cases as examined by electron microscopy and differential scanning calorimetry.

TEM observation of the morphology of alumina dendrites in a rapidly solidified Al203-25w/oZrO22 oxide alloy revealed three distinct dendrite morphologies corresponding to α-, γ- and δ- aluminas. STEM analysis showed the center of the α and γ dendrites to be solute poor, but the δ dendrite center to be solute rich, indicating possible solute trapping. Theoretical calculations show interface growth velocities in excess of 3m/sec.