Production of high chromium alloys TiC-Fe-Cr alloyed with silicon

Conclusions Sinterability and the mechanical properties of high-chromium alloys TiC—Fe—Cr can be considerably improved by alloying them with elements that act as surfactants and are oxidized more easily than chromium at temperatures of solid-phase and liquid-phase sintering. Such an element may be silicon.Translated from Poroshkovaya Metallurgiya, No. 5(281), pp. 65–69, May, 1986.     

Hot rolling of blanks from copper and nickel powders

Summary The authors investigated the hot rolling of preformed blanks from electrolytic copper and carbonyl nickel powders. The blanks were prepared by cold pressing, cold rolling, wedge pressing, and sintering loosely poured powder. The hot rolling was carried out in a special mill, in a hydrogen atmosphere. The investigation showed that at high rates of deformation, a rolling temperature of 0.8–0.9 T_melt, and a reduction of 50% the hot rolling of preformed copper and nickel blanks in one pass can yield strip with a relative density of 100%, a fine-grained structure, and mechanical properties which are not inferior to those of materials obtained by sintering powder compacts or cold-rolled strip.Translated from Poroshkovaya Metallurgiya, No. 6 (66), pp. 25–28, June, 1968.     

Filtration efficiency in casting of a complexly alloyed nickel melt

The use of a cellular ceramic filter is shown to be effective for casting nickel superalloys in vacuum, including superalloys cast using wastes. As a result of filtration, the volume fraction of nonmetallic inclusions and their sizes and quantity in a metal decrease.     

Structure of mechanically alloyed Ti-Al-Nb powders

Ti-Al-Nb ternary powder mixtures containing 24Al-11Nb, 25Al-25Nb, 37.5Al-12.5Nb, and 28.5Al-23.9Nb (at. pct) were mechanically alloyed in a SPEX 8000 mixer mill using a ball-to-powder weight ratio of 10:1. The structural evolution in these alloys was investigated by X-ray diffraction and transmission electron microscopy techniques. A solid solution of Al and Nb in Ti was formed at an early stage of milling, followed by the B2/body-centered cubic (bec) and amorphous phases at longer milling times. The stability of these phases and their transformation to other phases have been investigated by heat treating these powders at different temperatures. The B2/bcc phase transformed into an orthorhombic (O-Ti₂AlNb) or a mixture of the orthorhombic (O) and hexagonal close-packed (α₂-Ti₃Al) phases, the proportion of phases being dependent on the powder composition. Milling beyond the amorphous phase formation resulted in the formation of an fee phase in all the powders, which appears to be TiN, formed as a result of contamination of the powder. Formerly Graduate Student, University of Idaho     

Production of pipe blanks from corrosion-resistant duplex steel

The introduction of pipe-blank production (blank diameter 180 mm) from corrosion-resistant duplex steel (UNS S 31803, UNS S 32205, DIN 1.4462, and 03X22H5AM3) at PAO Dneprospetsstal’ plant is considered. The chemical composition of the melts at PAO Dneprospetsstal’ and pipe blank produced from duplex at traditional foreign suppliers is compared. The content of nonmetallic inclusions is studied, as well as the distribution and content of ferrite-austenite phases, the impact strength, the resistance to pitting corrosion, and the high-temperature deformability.     

NiAl powder alloys: I. Production of NiAl powders

The influence of five methods of production of Ni₅₀Al₅₀ powder alloys on the processes occurring during reactive alloy formation of nickel monoaluminide during heating is considered. It is shown that, when powder mixtures obtained by agitation in ball mills and cladded composite powders with a low level of internal stresses are used, it is possible to produce a material with a nearly equilibrium phase composition in the course of reactive sintering due to an exothermic effect with the participation of a liquid phase (aluminum melt) in the reaction. The sintered material is porous and has an island structure. Mechanical alloying in a high-energy ball mill (attritor) results in the formation of layered Ni/Al granules with a developed interface and a high level of internal stresses and defects, which makes it possible to decrease the temperatures of initiation of reactive interaction by ∼300°C. This interaction develops in the solid phase according to a slow diffusive mechanism leading to the formation of intermediate nickel aluminides and hindering the achievement of equilibrium phase composition. The microingot granules (∼80 wt % particles 100–400 μm in size) produced by melt spraying by gases (N, Ar) has the composition of the melt, but grain boundaries are depleted of aluminum in comparison with the volume. The NiAl powders (∼90 wt % particles <40 μm in size) produced by combined hydride-calcium reduction are characterized by a highly homogeneous nickel and aluminum distribution, and their composition is close to equilibrium. These two types of powders are selected as the initial material for investigating the compacting and production of NiAl-based alloys.     

Elevated-temperature stability of mechanically alloyed Cu-Nb powders

When two-phase mixtures of ductile metals are mechanically alloyed, they often assume a convoluted lamellar structure. Since these powders are consolidated at elevated temperatures, their structures (and, therefore, properties) are likely to be altered by consolidation processing. We have investigated microstructural changes that take place on heat-treating mechanically alloyed Cu −20 vol pct Nb alloys. The transition from a “platelike” to a spherical microstructure is described, and the kinetics of this process appear controlled by a type of boundary diffusion, even though the coarsening temperature was high in terms of the homologous temperature of Cu. Reasons for this behavior are suggested. Finally, during heat treatment (carried out in H), a Nb layer forms around the particles. The thickness of this layer (and the corresponding zone denuded of Nb within the particle) increases with continued elevated-temperature exposure, and at a rate consistent with the process being driven by curvature forces. Formerly Professor, Department of Materials Science and Engineering, University of Virginia, Charlottesville, VA     

Processing ductility of preheated blanks from titanium,copper, and aluminum powders

Powder Metallurgy and Metal Ceramics -     

Selection of powders for the production of porous blanks

Summary An analysis is made of experimental data on the relation between the porosity, particle size, filtration fineness, and coefficient of permeability of porous materials. A formula is derived for determining the coefficient of permeability from known values of porosity and particle size.Translated from Poroshkovaya Metallurgiya, No. 11 (47), pp. 9–13, November, 1966.     

Protective properties of detonation-deposited coatings from powders alloyed with aluminum and boron

Conclusions The corrosion resistance of detonation-deposited coatings from aluminum- and boron-containing PKh20N80 alloy, nickel, and stainless steel powders markedly surpasses that of constructional steel. The electrochemical properties of such detonation-deposited coatings are determined by their composition and thickness. The basis material is effectively protected against corrosion by 600-Mm-thick coatings. Under conditions of corrosive and mechanical wear detonation-deposited coatings from aluminum- and boron-containing 20% Cr-80% Ni alloy, nickel, and stainless steel powders operate satisfactorily under loads of not more than 5 MPa. The results of service tests have demonstrated the usefulness of detonation-deposited coatings from alloyed powders. Coating with powder of composition III was found to increase the useful life of certain parts of spraying equipment two to two and a half times.Translated from Poroshkovaya Metallurgiya, No. 8 (272), pp. 52–55, August, 1985.     

Shock consolidation of mechanically alloyed amorphous Ti-Si powders

Mechanical alloying was used to synthesize amorphous 5Ti-3Si atomic ratio powders in a SPEX mill under Ar atmosphere. X-ray diffraction analysis revealed formation of a single-phase amorphous compound after about 24 hours of milling. High-resolution transmission electron microscopy (TEM) showed that the milled powder still contained nanocrystallites of Ti and Si among regions of generally amorphous compound. The mechanically alloyed amorphous powder was shock consolidated, using a plate impact assembly, to produce bulk compacts. The compaction resulted in a significant amount of crystallization, forming 30- to 40-nm crystals of TiSi₂ and Ti₅Si₃ intermetallic compounds. The compacts were subsequently annealed above the crystallization temperature, measured to be ∼640 °C using differential thermal analysis. The compacts annealed at 800 °C for 1 hour showed only limited grain growth to ∼50-nm crystallite size. Microhardness of the shocked amorphous alloy compacts was ∼1100 KHN, which increased to ∼1250 KHN upon subsequent annealing, with the formation of a more homogeneous nanocrystalline microstructure. Formerly Undergraduate Research Assistant, School of Materials Science and Engineering, Georgia Institute of Technology. This article is based on a presentation made in the symposium “Dynamic Behavior of Materials,” presented at the 1994 Fall Meeting of TMS/ASM in Rosemont, Illinois, October 3-5, 1994, under the auspices of the TMS-SMD Mechanical Metallurgy Committee and the ASM-MSD Flow and Fracture Committee.