Effect of the method of producing Ni3Al-based alloy single crystals on the macro- and microhomogeneity of component distribution,structure, and properties

The mechanisms of hardening heterophase Ni₃Al-based cast alloys, which are thermally stable natural eutectic composites, are studied in the operating temperature range. The distribution of basic and alloying elements and impurities in macrovolumes along the height of a charge billet prepared in a vacuum induction furnace is analyzed. The effect of the deviation of the axis of intermetallic alloy single crystals from the 〈111〉 orientation on their mechanical properties is considered. It is shown that the deviation from this orientation within 2.5°–5.4° does not affect the short-term strength characteristics and substantially affects the ductility characteristics of the single crystals. The effect of the method of introducing basic components and refractory reaction- and surface-active alloying elements in the alloys on the structure-phase state of Ni₃Al-based alloys and their service life is investigated.     

Strength Improvement Through Grain Refinement of Intermetallic Compound at Al/Fe Dissimilar Joint Interface by the Addition of Alloying Elements

Dissimilar material joining between Al alloys and steel may be effective in decreasing the weight of automobile bodies. In this study, dissimilar lap joining of Al alloys containing certain alloying elements, such as Ni, Cr, Mn, Ti, or Si, to interstitial-free steel was performed by tungsten inert gas arc brazing, and the effect of the alloying element on the joint strength associated with the Al-Fe intermetallic compound layer at the dissimilar interface was examined. The addition of an appropriate amount of an alloying element to the alloy increased the joint strength; the addition of Ni exhibited the most effective improvement. The additions of some elements changed the grain structure of the η-Fe₂Al₅ layer but not its chemical composition. This is the first study to clarify that smaller grain size of η-Fe₂Al₅ correlated to greater strength of the Al/Fe dissimilar joint.     

Molybdenum in Nb-C alloys

The effects of molybdenum alloying additions to niobium on the carbide phases and their precipitation behavior were investigated. The experimental alloys included Nb-0.1C, Nb-15Mo-0.1C, and Nb-30Mo-0.1C. After selected heat treatments the microstructural changes were determined by metallography and the carbide phases were extracted and identified by X-ray diffraction and chemical analysis. The results are essentially in agreement with recent phase diagram determinations. Additions of 30 wt pct Mo appears to slightly increase the solubility of carbon in niobium at temperatures around 1650°C. The solubility of molybdenum in Nb₂C is very small. Discontinuous precipitation of β-Nb₂C was found to occur in the Nb-30Mo-0.1C alloy during annealing at 1200°C. The important, overall effect of molybdenum in Nb-C alloys is to decrease the rate of niobium carbide precipitation so that appreciable carbon supersaturation can be achieved even after comparatively slow furnace cooling.     

Structure and properties of boron-bearing iron granules for composites

The structure and properties of boron-bearing iron granules and composite materials based on them have been examined by metallography, x-ray structure analysis, microprobe analysis, and strength testing. It is shown that one should use iron borides cooled at rates of 10³–10⁴ deg/sec as finely divided fillers. Composites based on them are reliable and show wear resistance at the level of materials that contain tungsten carbides. Additional alloying of the iron borides with molybdenum and niobium increases the resistance of alloys for operation under conditions of gas-abrasive wear at room temperature, while alloying with chromium and vanadium does the same for elevated temperature.Dnepropetrovsk University. E. O. Paton Electric Welding Institute, Ukrainian Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurgiya, No. 2(362), pp. 45–49, February, 1993.     

Effect of alloying addition on structure and thermal stability of Ti40Al60 prepared by mechanical alloying

Ternary (Ti₄₀Al₆₀)₁₀₀−XM_X (X = 5–15 at., M = Mo, Nb) alloys have been prepared by Mechanical Alloying, and the process was monitored by X-ray diffraction technique. The effects of a third additional element have been examined concerning the alloying process, structure and phase thermal stability. As already observed in Ti₄₀Al₆₀ matrix prepared with the same conditions, an amorphous alloy was obtained at the end of the process. A different solubility of Mo (very limited) or Nb (total dissolved) into the matrix was detected. Upon thermal treatment the third element addition caused, in both cases, an increased crystallization temperature with respect to the matrix. The more detailed investigation on niobium addition (5–10 at.%) evidenced the following path for powder crystallization: amorphous-disordered Al-ordered L1₀ phase. The evolution of the long-range order parameter revealed that the disorder → order transition is favoured due to the presence of Nb, but independent of its concentration.     

Elastic Properties,Thermal Expansion Coefficients,and Electronic Structures of Mg and Mg-Based Alloys

Ab-initio density functional theory (DFT) calculations were performed to study alloying effects on hcp Mg. The alloy solid solution strengthening represented by bond strength enhancement in alloys, elastic properties, thermal expansion coefficients, and electronic structures of Mg-based alloys was investigated. Results show that alloying additions with sp-metal Al and rare earth (RE) Y are capable of increasing the bond strength, with the addition of Y achieving a better effect. The bond strength enhancement due to an RE Y addition is associated with a hybridization between the d-orbital of Y and the p-orbital of the Mg atoms near the Fermi energy, and this was consistent with the electron localized function (ELF) evaluations showing that more localized and stronger covalent bonds are formed between Y and Mg atoms. It is also found that alloying additions of Al, Zn, and Y are not capable of increasing elastic coefficients and moduli, indicating that bond strength enhancement could play a major role in alloy solid solution strengthening in Mg-based alloys. Possible reasons for the elastic properties accompanying the alloying addition are given from the electronic point of view. Furthermore, from the calculated negative Cauchy pressure (C ₁₃ – C ₄₄ < 0), it is concluded that the chemical bonds between Y and Mg atoms show angular characteristics.     

Rare-earth metals in nickel aluminide-based alloys: III. Structure and properties of multicomponent Ni<Subscript>3</Subscript>Al-based alloys

The possibility of increasing the life of heterophase cast light Ni₃Al-based superalloys at temperatures higher than 0.8T _m of Ni₃Al is studied when their directional structure is additionally stabilized by nanoprecipitates, which form upon additional alloying of these alloys by refractory and active metals, and using special methods for preparing and melting of an alloy charge. The effect of the method of introducing the main components and refractory reaction-active and surface-active alloying elements into Ni₃Al-based cast superalloys, which are thermally stable natural composite materials of the eutectic type, on the structure-phase state and the life of these alloys is studied. When these alloys are melted, it is necessary to perform a set of measures to form particles of refractory oxide cores covered with the β-NiAl phase and, then, γ′_prim-Ni₃Al phase precipitates during solidification. The latter phase forms the outer shell of grain nuclei, which provides high thermal stability and hot strength of an intermetallic compound-based alloy. As a result, a modified structure that is stabilized by the nanoprecipitates of nickel and aluminum lanthanides and the nanoprecipitates of phases containing refractory metals is formed. This structure enhances the life of the alloy at 1000 °C by a factor of 1.8–2.5.     

Effect of alloying additions on the structure and mechanical properties of Fe<Subscript>3</Subscript>Al -1C intermetallic alloy

Effect of titanium and nickel on the structure and properties of Fe₃Al intermetallic alloy containing about 1.0wt.% C have been investigated. The composition of the alloying element was substituted for Iron. The alloys were prepared by melting commercial grade raw materials iron, aluminum, titanium or nickel in air induction furnace with flux cover (AIMFC). Further these ingots were refined by electroslag refining (ESR) process. These ingots could be successfully hot-worked using conventional hot-forging and hot-rolling techniques. The hot-worked material was sound and free from cracks. ESR hot-rolled alloys were examined using optical microscopy, X-ray diffraction (XRD), scanning electron micrograph (SEM) to understand the microstructure of these alloys. The electron probe micro analysis (EPMA) studies were carried out to determine the matrix and precipitate compositions and to identify the phases present in the alloys. The base alloy and the alloy containing Ni exhibited a two-phase microstructure of Fe₃AlC_0.5 precipitates in Fe₃Al matrix. The alloy containing Ti exhibits three-phase microstructure, the additional phase being TiC precipitate. Ti addition resulted in no improvement in strength at room temperature and at 873 K whereas Ni addition has resulted in greater improvement in strength at room temperature and at 873 K and also improved the creep life significantly from 66 hrs to 111 hrs.     

Structure and mechanical properties of chromium alloyed with magnesia and boron

Conclusions By alloying chromium simultaneously with magnesia and borides, it is possible to increase its high-temeprature strength and at the same time improve its low-temperature ductility. The best combination of mechanical properties is exhibited by alloys with boron contents of not more than 0.1 wt. %. The greatest increase in the short-time strength of chromium is brought about by alloying with tungsten. In longer periods of operation higher strength is shown by chromium alloyed with vanadium boride.Translated from Poroshkovaya Metallurgiya, No. 7(223), pp. 78–82, July, 1981.     

Nanocomposites of Aluminum Alloys by Rapid Solidification Processing

Aluminium alloys reinforced with transition metal aluminide (Al₃Ti, Al₃Fe, Al₃Ni, etc.) particles possess high specific strength both at ambient and elevated temperature. The improved strength of these alloys are the results of slower coarsening rate of the intermetallic particles due to low diffusivity of the transition metals in aluminium. However, the strength can be enhanced further by refining the microstructure of the alloys to nanometer range. The authors have successfully attempted two important non-equilibrium processing techniques i.e. rapid solidification processing (RSP) and mechanical alloying for the refinement of the microstructure in various aluminium alloys. In this report, authors present a short review of their work on RSP of Al?CTi and Al?CFe alloys to produce nanocomposites.     

Preparation of TiAl15Si15 intermetallic alloy by mechanical alloying and the spark plasma sintering method

This work is devoted to the preparation of alloys based on intermetallic compounds in the Ti–Al–Si system by powder metallurgy using mechanical alloying and the spark plasma sintering (SPS) method. The aim was to describe the formation of intermetallic phases during mechanical alloying of TiAl15Si15 (wt-%) alloy and to consolidate the powder prepared by optimised conditions. Phase composition, microstructure and hardness of compacted alloy were determined. Four hours of mechanical alloying is sufficient time for preparation of pure elements free material composed only of intermetallic phases. After consolidation, the TiAl15Si15 alloy has a homogeneous structure composed of silicide (Ti₅Si₃) in aluminide (TiAl) matrix. The hardness of the material reaches 865?±?42 HV 5.     

Effect of the phase composition and structure of titanium alloys on their interaction with nitrogen during low-temperature ion nitriding

The interaction of nitrogen with commercial titanium alloys having a single-phase α (VT1-0, VT5 alloys) or β (TS6 alloy) structure and a two-phase α + β structure with various contents of the β phase (VT20, VT6, VT3-1, VT23, VT22) is studied during ion nitriding at 550 and 600°C. The initial phase composition, the degree of phase alloying, and the structure have been shown to substantially affect the length of the diffusion zone having an α_N structure and the amounts of the Ti₂N (ε phase) and TiN (δ phase) surface nitrides. A group of alloys containing up to 30% β phase in an α + β structure is separated. These alloys are of interest as a basis for designing surface gradient structure materials using surface nitrogen alloying upon low-temperature ion nitriding.     

Microstructure and Hardness Properties Investigation of Ti and Nb Added FeNiAlCuCrTi x Nb y High Entropy Alloys

Properties of pure metals can be enhanced by alloying with other metallic or non-metallic elements according to the need. However, as multiple alloying elements in an alloy may lead to the formation of many intermetallic compounds with complex microstructures and poor mechanical properties, new types of metallic alloys called high entropy alloys with at least five elements with equimolar ratios were developed. In this study, FeNiAlCuCrTi _x Nb _y (x, y = 0, 0.5, 1.0, 1.5) alloys have been prepared using Ar arc melting technique. Microstructural studies using scanning electron microscope and XRD showed that Ti addition promoted secondary BCC₂ phase whereas, Nb acted as FCC stabilizer. Samples with combined Nb and Ti addition showed FCC₁ and FCC₂ structure with Nb-rich FCC₂ dendritic phase as dominant phase. Though, individual Nb and Ti additions have resulted in increased hardness, combined additions have resulted in highest hardness of 797 HV under 1 kg load.     

Influence of zirconium addition on the microstructure,thermodynamic stability,thermal stability and mechanical properties of mechanical alloyed spark plasma sintered (MA-SPS) FeCoCrNi high entropy alloy

ABSTRACT

Equiatomic FeCoCrNi (Zr₀) and non-equiatomic FeCoCrNiZr_0.4 (Zr_0.4) high-entropy alloys (HEAs) were synthesised by mechanical alloying and spark plasma sintering. XRD analysis verified the formation of FCC and BCC solid solution phases in both alloys after 30?h of ball milling. While the SPS FeCoCrNi alloy contains both FCC and BCC solid solution phases, the FeCoCrNiZr_0.4 presents an FCC solid solution. The thermodynamic analysis showed that FeCoCrNiZr_0.4 is more stable with respect to the FeCoCrNi alloy. The phase stability of FeCoCrNiZr_0.4 was revealed up to ～800°C. The shear strength and hardness of the FeCoCrNi HEA improved with Zr addition. Failure analysis of the shear punch tested samples revealed a ductile fracture with dimple structure for FeCoCrNi and a brittle fracture with a smooth featureless surface for FeCoCrNiZr_0.4.     

Effect of Chemical Composition on Susceptibility to Weld Solidification Cracking in Austenitic Weld Metal

The influence of the chemical composition, especially the niobium content, chromium equivalent Cr_eq, and nickel equivalent Ni_eq, on the weld solidification cracking susceptibility in the austenite single-phase region in the Schaeffler diagram was investigated. Specimens were fabricated using the hot-wire laser welding process with widely different compositions of Cr_eq, Ni_eq, and niobium in the region. The distributions of the susceptibility, such as the crack length and brittle temperature range (BTR), in the Schaeffler diagram revealed a region with high susceptibility to solidification cracking. Addition of niobium enhanced the susceptibility and changed the distribution of the susceptibility in the diagram. The BTR distribution was in good agreement with the distribution of the temperature range of solidification (ΔT) calculated by solidification simulation based on Scheil model. ΔT increased with increasing content of alloying elements such as niobium. The distribution of ΔT was dependent on the type of alloying element owing to the change of the partitioning behavior. Thus, the solidification cracking susceptibility in the austenite single-phase region depends on whether the alloy contains elements. The distribution of the susceptibility in the region is controlled by the change in ΔT and the segregation behavior of niobium with the chemical composition.     

Phase stability and mechanical properties of carbide and boride strengthened chromium-base alloys

Phase stability and mechanical properties of five carbide and two boride strengthened chromium-base alloys are presented. Compositions examined were Cr-0.5 TaC (mole pet), Cr-0.5 TiC, Cr-0.5 Cb(Nb)C, Cr-0.5 HfC, Cr-0.5 ZrC, Cr-0.5 CbB, and Cr-0.5 TaB. A transition in stability from the carbide of the principal alloying metal to Cr₂₃C₆, complete at approximately 2800°F, occurs in the Cr-0.5 TaC, Cr-0.5 TiC, and Cr-0.5 CbC alloys. Similarly, a change in phase stability from borides of columbium (niobium) and tantalum to Cr₄B occurs at ∼2800°F in the Cr-0.5 CbB and Cr-0.5 TaB compositions. The compounds HfC and ZrC, respectively, remained stable in the Cr-0.5 HfC and Cr-0.5 ZrC alloys at this temperature. Stress-rupture properties at 2100°F improved for several alloys when aged at this temperature to precipitate the carbide or boride of the principal alloying metal following higher temperature heat treatment to form the Cr₂₃C₆ or Cr₄B phases. Rupture life of the Cr-0.5 TaC alloy, for example, was increased at 15 ksi and 2100°F from 4 hr for as-fabricated material, to 186 hr after heat treatment. Improvement of rupture life for similar material and test conditions from 24 hr to 382 hr was observed in the Cr-0.5 TaB composition.     

Prospects of raising the heat resistance of materials based on refractory metals

Conclusions The paper examines the principles underlying the effective alloying of refractory metals on the basis of the strength loss mechanism. The heat resistance of rhenium, whose strength loss occurs essentially during recrystallization, can be increased by alloying on the basis of the principles which have been utilized for developing aluminum, cobalt, and nickel alloys.Other refractory metals (tungsten, molybdenum, niobium) lose most or all of their strength before recrystallization, as a result of polygonization processes. The heat resistance of these refractory metals and their alloys can be increased by inhibiting the polygonization process. The mechanisms by which additions influence the rate of polygonization are discussed.Translated from Poroshkovaya Metallurgiya, No. 8(44), pp. 38–42, August, 1966.     

Influence of alloying elements and grain refiner on microstructure,mechanical and wear properties of Mg-Al-Zn alloys

In the present investigation, the effects of alloying elements (Sn, Pb) and grain refiner (Ag, Zr) on microstructure, mechanical and wear properties of as-cast Mg-Al-Zn alloys were studied. The alloys were prepared through melting-casting route under a protective atmosphere and cast into a permanent mould. The microstructure of the base alloy consisted of α-Mg, Mg₁₇Al₁₂ continuous eutectic phase at the grain boundary and Mg-Zn phase was distributed within the grains. Addition of Sn and Pb suppressed the formation of continuous Mg₁₇Al₁₂ eutectic phase and formed Pb enriched Mg₂Sn precipitates at the grain boundary as well as inside the grain. The Ag and Zr addition to Mg-Al-Zn-Sn-Pb alloy suppressed the Mg₁₇Al₁₂ phase formation and refined the grains leading to improve mechanical properties. Addition of Sn, Pb and grain refiner (Ag, Zr) significantly enhanced the tensile strength and elongation but reduced hardness. The Ag addition imparted best tensile properties, where ultimate tensile strength (UTS) and elongation are 205?MPa and 8.0%, respectively. The fracture surfaces were examined under SEM which revealed cleavage facets and dimple formation. Therefore, the cleavage fracture and dimple rupture were considered as the dominant fracture mechanisms for developed Mg alloys. The cumulative volume loss of Mg alloys increased with sliding distance and applied load. The coefficient of friction decreased with sliding distance. The microscopic observation, analysis of the wear surface and coefficient of friction revealed that the wear mechanism of developed Mg alloys changes from abrasion oxidation to delamination wear.     

An investigation of the fracture and fatigue crack growth behavior of forged damage-tolerant niobium aluminide intermetallics

The results of a recent study of the effects of ternary alloying with Ti on the fatigue and fracture behavior of a new class of forged damage-tolerant niobium aluminide (Nb₃Al-xTi) intermetallics are presented in this article. The alloys studied have the following nominal compositions: Nb-15Al-10Ti (10Ti alloy), Nb-15Al-25Ti (25Ti alloy), and Nb-15Al-40Ti (40Ti alloy). All compositions are quoted in atomic percentages unless stated otherwise. The 10Ti and 25Ti alloys exhibit fracture toughness levels between 10 and 20 MPa√m at room temperature. Fracture in these alloys occurs by brittle cleavage fracture modes. In contrast, a ductile dimpled fracture mode is observed at room-temperature for the alloy containing 40 at. pct Ti. The 40Ti alloy also exhibits exceptional combinations of room-temperature strength (695 to 904 MPa), ductility (4 to 30 pct), fracture toughness (40 to 100 MPa√m), and fatigue crack growth resistance (comparable to Ti-6Al-4V, monolithic Nb, and inconnel 718). The implications of the results are discussed for potential structural applications of the 40Ti alloy in the intermediate-temperature (∼700 °C to 750 °C) regime.     

Microstructure and properties of Ni<Subscript>3</Subscript>Si alloyed with Cr fabricated by self-propagating high-temperature synthesis casting route

Ni₃Si alloys with 20, 30, and 40 wt pct Cr were fabricated by self-propagating high-temperature synthesis casting at 543 K. Thermite reaction (Cr₂O₃+5CrO₃+12Al=7Cr+6Al₂O₃) was used in Cr alloying. The method is simple and economical when used to prepare Ni₃Si-based alloys. The process is described in detail. The alloys were analyzed with X-ray diffraction (XRD) and scanning electron microscopy (SEM) with X-ray energy dispersive spectroscopy (EDS). The results showed the alloys mainly consisted of Ni₃Si and Ni₅Si₂ with dissolved Cr and Cr phases. Phases and microstructures of the alloys varied with Cr content. Microhardness, bending and compressive strength, and wear rate of the alloys were measured. Microhardness of the alloys was higher than that of Ni₃Si without Cr and increased with Cr content. Bending and compressive strength of the alloys were better than those of the Ni₃Si without Cr, and those of the alloy with 30 wt pct Cr were the highest. The wear rate of the alloys was lower than that of the Ni₃Si without Cr and decreased with Cr content.