Alan Irwin Taub

Boron extended solubility and strengthening potency in rapidly solidified Ni3Al

Abstract The strengthening of the intermetallic compound Ni3Al by boron addition has been investigated via the rapid solidification technique of melt spinning. Using X-ray diffraction, differential thermal analysis and transmission electron microscopy it is shown that by rapid solidification up to 1.5 at.% boron can be held in solution in the aluminide without formation of boride. The lattice parameter results further show that the boron atoms in solution tend to occupy the interstitial sites, generate large lattice strain, and thereby strengthen the Ni3Al substantially. For example, addition of 1 at.% boron increases the room temperature yield strength of rapidly solidified Ni3Al from ∼480to∼750MPa. This represents a strengthening potency significantly larger than that of substitutional solutes.

Intermetallic compounds for high-temperature structural use

The next generation of efficient turbines and engines will require materials that can withstand operating temperatures approaching 2000�C. Intermetallic compounds with high melting temperatures are candidates for this application, but the obstacle of their limited ductility must first be overcome. Because the available data on these materials is limited, a survey of the effects of chemistry and crystal structure must be performed. With the use of melting temperature and density as figures of merit, the most likely candidates have been identified for preliminary screening.

Composition dependence of ductility in boron-doped, nickel-base L12 alloys

The effect of boron doping on the ductility and fracture morphology of the Ni/sub 3/X(X=Al, Ga, Si, Ge) system has been examined. For the boron-doped binary alloys, the ductility varies as Ni/sub 3/Alapprox. =Ni/sub 3/Ga>Ni/sub 3/Ge. The boron-doped ternary alloys follow the same trend of decreasing ductility with increasing Si and Ge content. The data is consistent with both the valency/size effect and electronegativity models for grain boundary cohesive strength.

Ductility in boron-doped, nickel-base L12 alloys processed by rapid solidification

Etude de la ductilite dans les composes intermetalliques de type Ni 3 X (ou X=Al, Ga, Si, Ge) de structure ordonnee L1 2 en fonction de la teneur en bore (0,1 a 1% at.)

Carbon effects in rapidly solidified Ni 3 Al

The effect of carbon on the mechanical properties of ordered, face-center-cubic Ni 3 Al has been studied. It has been found that carbon provides no ductihzation to the intermetallic compound, but exerts a large solid solution strengthening effect. The strengthening rate measured is Δσ y /ΔC∼0.5 G per atom percent carbon, where G is the Ni 3 Al shear modulus. Auger analysis and lattice parameter measurements were also carried out. The results are discussed with respect to the nature of carbon in grain boundary regions and in the bulk.

Grain boundary segregation of boron and sulfur and its effect on ductility in rapidly solidified Ni-base L12 compounds

Abstract This paper reports a study of boron segregation in Ni 3 Al, Ni 3 Si, Ni 3 Ge, and Ni 3 Ga. Sulfur segregation in Ni 3 Al is also considered. The results show that boron segregates in Ni 3 Al and that the amount of segregation tends to increase as the bulk concentration of boron in the alloy increases. However, because the samples had not reached equilibrium during the heat treatment, there was some scatter in this correlation. Boron also segregated in Ni 3 Si and Ni 3 Ge, but there appeared to be no dependence of the amount of segregation on the bulk concentration. This result is not surprising because in these alloys the boron concentration was above the solubility limit. Boron segregation also occurred in Ni 3 Ga and it appeared to increase with increasing bulk concentration. However, only a small amount of data was obtained for this system. Sulfur segregated in Ni 3 Al and its concentration on the grain boundaries increased with increasing bulk concentration. It did not appear to compete with boron for grain boundary sites. Aluminum also segregated in Ni 3 Al, but there was a large amount of scatter in the data. The plastic strain to failure measured for the samples of Ni 3 Al did not correlate with the amount of boron segregation. In particular, we could not explain the fact that boron additions enhance grain boundary cohesion more effectively in Ni-rich alloys by an increase in boron segregation in these alloys. Stoichiometric alloys and Ni-poor alloys that were very brittle had boron segregation in equivalent amounts to that found in ductile Ni-rich alloys.

Improved ductility of Ni3Si by microalloying with boron or carbon

The effects of boron and carbon additions on the tendency for intergranular fracture in trinickel silicide intermetallics are reported. Melt spinning of Ni77Si23 alloyed with 0.1 at. pet boron results in full bend ductility and complete transgranular fracture compared with brittle intergranular fracture for the unmodified compound. Alloying with 0.1 at. pet carbon also produces full bend ductility but a mixed mode failure (≈30 pct transgranular). For both carbon and boron additions, reducing the Ni concentration of the base compound results in a greater percentage of intergranular fracture. The boron solubility limit depends on the Ni concentration of the base compound. For Ni77Si23, the solubility limit is between 0.1 and 0.2 at. pet boron. For compounds with silicon concentrations of 23.5 and 24.0 at. pct, the solubility limit is less than 0.1 at. pct boron. Boron additions above the solubility limit result in Ni3B precipitates which degrade the bend ductility and increase the percentage of integranular fracture. Alloying with carbon above the solubility limit (<0.1 at. pct) produces graphite precipitation. For Ni77Si23, increasing the carbon concentration from 0.1 to 1.0 at. pct resulted in no change in the ductility. Auger examination of the grain boundary composition showed strong segregation of both boron and carbon. Enrichment in silicon concentration was also observed.

Selecting high-temperature structural intermetallic compounds: The materials science approach

Some 300 intermetallic compounds with high melting temperatures are candidate materials for the high-temperature turbines and engines of the future. Before these applications can be realized, however, the limited ductility of intermetallic materials must be overcome. Using melting temperature and density as figures of merit, and considering the effects of composition and crystal structure, the most likely candidates for these high-performance applications may be identified.

CRYOGENIC PROPERTIES OF A P/M Ni3Al-B ALLOY

Polycrystalline Ni/sub 3/Al-based intermetallic alloys have overcome their room temperature brittleness problem with a small amount or boron addition. Because of their unique strength-temperature relationship and good oxidation resistance at high temperatures, research efforts have been concentrated extensively on structural applications at elevated temperatures. In this paper the authors show that ductile Ni/sub 3/Al-B alloys also exhibit remarkable mechanical properties at cryogenic temperatures.

Property Comparison of Melt-Spun Ribbons and Consolidated Powders of Ni 3 A1-B

Ductile intermetallic Ni 3 Al-B alloys have been processed through three rapid solidification techniques: melt spinning, gas atomization, and plasma deposition. Different thermal treatment was required for each rapidly solidified product to form samples for mechanical evaluation. Melt-spun ribbons were tested in ribbon form in the as-cast or annealed conditions, while atomized powders were tested after consolidation by hot isostatic pressing (HIP) or low pressure plasma deposition. Alloy strength, as well as tensile ductility, was found to depend strongly on processing technique, thermal treatment, sample geometry, and most importantly, alloy chemistry. Microstructural and fractographic observations indicate that grain boundary brittleness caused by material processing history plays the major role in determining the alloys mechanical behavior.