Assessment and modelling of isothermal forging of intermetallic compounds. Part 3 – Ni3Al

Abstract

An alloy based on Ni₃(Al, Cr), IC­264, has been isothermally forged in the temperature range 950–1100°C and strain rate range 3×10^-4 to 3.5×10^-2 s^-1. Stress–strain curves show flow softening for most forging conditions, suggesting dynamic recrystallisation, as does microstructural examination. Deformation modelling has been carried out using a simple constitutive relationship.     

Effect of Ni on the wear behavior of a zinc-aluminum alloy

In this investigation, an attempt has been made to examine the effect of Ni on the wear response of a high-aluminum zinc alloy. The alloy has been modified with 0.3 and 0.9 wt% Ni, and wear tests have been carried out at sliding speeds of 3.925 and 6.54 m/s. The wear characteristics have been correlated with their microstructural features. The unmodified alloy exhibits inferior wear behavior with the increase in sliding speed. The improved wear response of the modified alloys is due to the presence of Ni₃Al phase formed throughout the matrix. Moreover, the improvement of the modified alloy is more significant at the higher speed of sliding and also with the increase in Ni content. This study indicates that it is possible to develop modified versions of high-aluminum zinc-based alloys having much improved wear characteristics; the information gains special attention in view of the high speed of sliding used in this study.     

Effect of 0.1% vanadium addition on precipitation behavior and mechanical properties of Al-6063 commercial alloy

The effect of 0.1 wt% vanadium additions on the precipitation behavior and the mechanical properties of a commercial Al-6063 alloy were studied. A master alloy containing 3 wt% V was added during casting. The cast ingot was homogenized, extruded and cooled employing two different cooling modes: forced air and water. Further aging was carried out following the standard T5 and T6 treatments for alloys with and without vanadium. The microstructural characterization, mechanical properties, and fractografic study were carried out. The addition of 0.1% vanadium to Al-6063 alloy under T5 treatment, accelerates the precipitation kinetics of β″ and β′ phases. The alloys with and without vanadium under T6 show a similar behavior, the co-existence of β′ and β″ precipitation is observed in both alloys. In general, vanadium additions to Al 6063 have a detrimental effect on the mechanical properties, showing only a beneficial effect for certain specific conditions.     

Effect of silicon,magnesium, cobalt and iron additions on the microstructure of Al-Li centrifugally atomized powders

The effect of the addition of silicon (up to 4 wt%), magnesium (up to 7.25 wt%), cobalt (up to 0.8 wt%) and iron (up to 1.5 wt%) on the microstructure of as-solidified Al-3 wt% Li powders, produced by centrifugal atomization in a helium atmosphere, has been studied by means of optical, scanning electron and transmission electron microscopy. The results show that the microstructure changes from dendritic in the case of Al-Li and Al-Li-Mg alloys to a eutectic (Al + AlLiSi) mixture in the Al-Li-Si alloy to a cellular structure for the Al-Li-Co alloy, and results in the direct nucleation of coarse intermetallic Al₆ Fe from the melt followed by subsequent growth in the case of Al-Li-Fe alloy.     

Laser cladding of zirconium on magnesium for improved corrosion properties

Laser cladding of Mg-2 wt% Zr, and Mg-5wt% Zr powder mixture onto magnesium was carried out. The microstructure of the laser clad was studied. From the microstructural study, the epitaxial regrowth of the clad region on the underlying substrate was observed. Martensite plates of different size were observed in transmission electron microscope for Mg-2wt% Zr and Mg-5wt% Zr laser clad. The corrosion properties of the laser clad were evaluated in sea-water (3.5% NaCl). The position of the laser claddings in the galvanic series of metals in sea-water, the anodic polarization characteristics of the laser claddings and the protective nature and the stability of the passivating film formed have been determined. The formation of pitting on the surface of the laser clad subjected to corrosion has been reported. The corrosion properties of the laser claddings have been compared with that of the commercially used magnesium alloy AZ91 B.     

Carbon nanotube reinforced aluminum nanocomposite via plasma and high velocity oxy-fuel spray forming

Free standing structures of hypereutectic aluminum-23 wt% silicon nanocomposite with multiwalled carbon nanotubes (MWCNT) reinforcement have been successfully fabricated by two different thermal spraying technique viz Plasma Spray Forming (PSF) and High Velocity Oxy-Fuel (HVOF) Spray Forming. Comparative microstructural and mechanical property evaluation of the two thermally spray formed nanocomposites has been carried out. Presence of nanosized grains in the Al-Si alloy matrix and physically intact and undamaged carbon nanotubes were observed in both the nanocomposites. Excellent interfacial bonding between Al alloy matrix and MWCNT was observed. The elastic modulus and hardness of HVOF sprayed nanocomposite is found to be higher than PSF sprayed composites.     

Interface and fracture of carbon fibre reinforced Al-7 wt% Si alloy

The interface structure in an aluminium-7 wt% silicon alloy reinforced with carbon fibres has been investigated using analytical electron microscopy. Crystals of aluminium carbide (Al₄C₃) have been identified in interface regions and their structure and growth are discussed. Mechanical properties of the composite have been measured and fracture behaviour studied using acoustic emission analysis in parallel with microstructural examination. The results indicated that the aluminium carbide interfacial reaction had produced a strong fibre matrix bond, but reduced the fibre strength and embrittled the matrix. Consequently, whole fibre bundles failed in a brittle manner in the longitudinal direction with limited pull-out of individual fibres. The findings are discussed in relation to the method used to manufacture the composite.     

Effect of primary alpha phase variation on mechanical behaviour of Ti–6Al–4V alloy

Small punch tests (SPTs) have been carried out at room temperature to correlate the microstructural variation of Ti–6Al–4V alloy with that of SPT parameters. Microstructural variation in terms of different volume fractions of primary alpha phase of Ti–6Al–4V alloy has been introduced as a result of solution annealing at different temperatures followed by thermal aging. Small punch test parameters, i.e. total area under the load vs displacement curve, area under the zone of elastic bending, plastic bending and plastic instability have been found to increase from the content of 10% primary alpha phase to 20% primary alpha phase and then these are decreasing from the content of 20% primary alpha phase to 30% primary alpha phase.     

Effect of ball milling time on the structural characteristics and mechanical properties of nano-sized Y2O3 particle reinforced aluminum matrix composites produced by powder metallurgy route

Mechanical milling presents an effective solution in producing a homogenous structure for composites. The present study focused on the production of 0.5 wt% yttria nanoparticle reinforced 7075 aluminum alloy composite in order to examine the effects of yttria dispersion and interfacial bonding by ball milling technique. The 7075 aluminum alloy powders and yttria were mechanically alloyed with different milling times. The milled composites powders were then consolidated with the help of hot pressing. Hardness, density, and tensile tests were carried out for characterizing the mechanical properties of the composite. The milled powder and the microstructural evolution of the composites were analyzed utilizing scanning and transmission electron microscopy. A striking enhancement of 164% and 90% in hardness and ultimate tensile strength, respectively, were found compared with the reference 7075 aluminum alloy fabricated with the same producing history. The origins of the observed increase in hardness and strength were discussed within the strengthening mechanisms' framework.     

Influence of microstructure of (α+β) Ti-6.2.4.6 alloy on high-cycle fatigue and tensile test behaviour

Tensile and gigacyclic fatigue behaviour of Ti–6Al–2Sn–4Zr–6Mo alloy were investigated as a function of lamellar primary α- and β-transformed microstructures. Three thermomechanical processes (TP1, TP2, TP3) were selected to produce different combinations of microstructural features on two slightly different compositions of the alloy (A and B). Ultrasonic fatigue tests were performed in air and liquid nitrogen at a frequency of 20 kHz ( R = −1, T  = 300 and 77 K), giving fatigue tests up to 10⁹ cycles. Microstructural features and the fracture initiation dependence on the primary α lamellar phase were observed by SEM and/or characterized by quantitative image analysis. It has been found that the microstructure of alloy B produced by TP1 represents a better compromise between resistance to initiation and resistance to microcrack growth. Quicker initiation occurs in coarser α-platelets (TP2, alloy B), and the continuous partially transformed β matrix appears to effectively decrease the tensile and HCF resistance. The bimodal structure (TP3, alloy B) has the best resistance at room temperature, but the presence of a coarse globular phase decreases this fatigue resistance at low temperature.     

球磨Zr7Ni10合金提高Zr基电极合金的电化学性能

为了提高合金的放电容量和高倍率放电性能，通过球磨Zr7Ni10合金对Zr0．5Ti0．5Mn0．7V0．2Co0．1Ni1．2合金表面进行改性，并研究了不同Zr，Ni10量和球磨时间对合金的相结构和电化学性能的影响。当采用8％（质量分数）Zr，Ni10进行球磨1h后，合金仍保持晶态，在50mAh／g电流条件下经过9次循环达到最大放电容量266mAh／g，比未球磨合金提高了约20％，而且在300mA／g电流条件下仍能保持最大放电容量的85%。随着球磨时间的增加，合金逐渐转为非晶态，合金的放电容量也迅速降低。非晶化合金在800℃进行热处理后大部分重新晶化，经过22次循环达到最大放电容量200mAh／g。     

Age Hardening Behavior of Wrought Al-Mg-Sc Alloy

Ageing of Al-6Mg alloy doped with varying concentration of scandium ranging from 0.2 wt% to 0.6 wt% has been carried out. Cold-rolled alloy samples are isochronally aged for 60 minutes at different temperatures. The cast and hot-rolled samples are also aged isochronally for 90 minutes at different temperatures up to 450°C. Isothermal ageing of cold-rolled samples is conducted at various temperatures for different periods of time ranging from 30 to 480 minutes. Hardness values of the differently processed alloys have been measured to understand the ageing behavior of Al-6Mg alloy with scandium addition. The hot-rolled alloys after ageing do not show any hardening response due to ageing. Ageing of cold-rolled alloys envisaged precipitation of Al₃Sc which is not noted to be dislocation induced. The kinetics of precipitation of Al₃Sc in Al-6Mg-Sc alloys are found to be controlled by the diffusion of scandium in aluminum.     

Synthesis characterization and hydrogen absorption studies of the composite materials La2Mg17–x wt% LaNi5

The composite materials La2Mg17–x wt% LaNi5 have been synthesized with various values of x, and the hydrogenation behaviour of these materials has been extensively studied. The as-synthesized materials were activated by heating the materials at about 360±10°C temperature under a hydrogen pressure of 33 kg cm-2 for nearly 6 h. The maximum hydrogen storage capacity was found to be 5.3 wt% for the composite material La2Mg17–10 wt% LaNi5 at 400±10°C temperature. This is one of the very highest storage capacities known so far. The initial rate of hydrogen absorption of La2Mg17–10 wt% LaNi5 was found to be 20 cm3 g-1 min-1 (at 400±10°C temperature). In order to elucidate the influence of LaNi5 addition, which significantly accelerated the hydriding rate and hydrogen storage capacity of La2Mg17, structural–microstructural characterization and chemical analysis of the composite materials employing X-ray diffraction, scanning electron microscopy and energy dispersive analysis of X-rays techniques have been carried out.     

Effects of boron addition on a melt-spun Ni-base superalloy

Melt spinning of a nickel-base superalloy containing various amounts of boron up to 3.0 wt% has been carried out to explore the potential of extended boride alloyability through rapid solidification. More specifically, the melt-spinning castability, ribbon-solidification microstructure and heat-treatment precipitation were studied as a function of boron concentration by using analytical electron microscopy and a number of other techniques. Special attention was given to the boride structure, chemistry and thermal stability. The microstructural observations were then correlated to the ribbon bend ductility tested in as-cast and annealed conditions. On the basis of the present results, future investigation of superalloys using the rapid solidification process and the boride alloying concept is discussed.     

Creep-induced phase transformations in furnace cooled Zn-Al alloy

Phase transformation and microstructural change of a furnace-cooled eutectoid Zn-Al alloy specimen (76 wt% Zn-22 wt% Al-2 wt% Cu) were investigated during creep testing by using scanning electron microscopy and X-ray diffraction techniques. Creep-induced decomposition of a metastable η′T phase and a four-phase transformation, α+ε→T′+η, occurred during the creep testing. Also microstructural change was observed from a lammellar structure partially into a spheroidized structure in the rupture part of the furnace-cooled alloy. The mechanism of the creep rupture of the furnace-cooled eutectoid Zn-Al alloy was also discussed. This revised version was published online in November 2006 with corrections to the Cover Date.     

Magnetic domain structure of isotropic MnAlC permanent magnet alloys

Observations of the magnetic domain structure were made on an isotropic MnAlC alloy (of the following composition: 73.0 wt% manganese, 26.4 wt% aluminium and 0.6 wt% carbon) homogenized at 1373 K for 1 h, quenched in water and tempered in the temperature range from 723 to 923 K. Observation of the magnetic domain structure was carried out by the Bitter powder pattern technique. It was found that the magnetic properties of the MnAlC alloy are closely related to the type of magnetic domain structure.     

Investigation of dual phase transformation of commercial low alloy steels: Effect of holding time at low inter-critical annealing temperatures

Dual phase steels are a class of steels characterized by a microstructure consisting of a soft ferrite matrix with hard martensite islands at the grain boundaries. The temperature in the dual phase (α + γ) region and the holding time are two important parameters in the intercritically annealing process. In this study, different grades of commercial low alloy steels have been heat treated to a constant annealing temperature by changing the holding time. It is observed that the effect of holding time is dependent on the steel composition. In this context, a microstructural examination has been carried out using optical, scanning electron microscope and electron probe micro-analysis and hardness values have been determined.     

Effect of heat treatment on strength and abrasive wear behaviour of Al6061-SiC<Subscript>p</Subscript> composites

In recent years, aluminum alloy based metal matrix composites (MMC) are gaining importance in several aerospace and automobile applications. Aluminum 6061 has been used as matrix material owing to its excellent mechanical properties coupled with good formability and its wide applications in industrial sector. Addition of SiC_p as reinforcement in Al6061 alloy system improves its hardness, tensile strength and wear resistance. In the present investigation Al6061-SiC_p composites was fabricated by liquid metallurgy route with percentages of SiC_p varying from 4 wt% to 10 wt% in steps of 2 wt%. The cast matrix alloy and its composites have been subjected to solutionizing treatment at a temperature of 530°C for 1 h followed by quenching in different media such as air, water and ice. The quenched samples are then subjected to both natural and artificial ageing. Microstructural studies have been carried out to understand the nature of structure. Mechanical properties such as microhardness, tensile strength, and abrasive wear tests have been conducted both on matrix Al6061 and Al6061-SiC_p composites before and after heat treatment. However, under identical heat treatment conditions, adopted Al6061-SiC_p composites exhibited better microhardness and tensile strength reduced wear loss when compared with Al matrix alloy.     

Corrosion behaviour of aluminium-based metal matrix composites

The corrosion characteristics, in 3.5 wt% NaCl solution, of aluminium alloy composites containing a range of reinforcements have been investigated using potentiostatic measurements and simple immersion tests. Complementary microstructural studies carried out on corroded surfaces and sections through corroded material have identified a number of preferential corrosion sites; these include the fiber/matrix interface, especially where it contains chemical reaction products resulting from composite fabrication, as well as second phases and pores in the metal matrix. The effect on corrosion behaviour of the different reinforcements, with particular reference to their chemistry and geometry, is discussed, as is the influence of composite manufacturing route.     

Stress corrosion cracking susceptibility of ultrafine grained AZ31

In this study, stress corrosion cracking (SCC) behavior of AZ31 magnesium alloy was carried out using slow strain rate testing (SSRT) technique in 3.5 wt% NaCl solution. The influence of microstructural scale on the stress corrosion behavior was investigated in AZ31 alloy with three different mean grain sizes. Single-pass and two-pass friction stir processing (FSP) was employed to obtain fine grain and ultrafine grain microstructures, respectively. For FSP, SSRT specimens were extracted from the processed region. SSRTs were carried out in air and solution at an initial strain rate of 10⁻⁶/s. A significant decrease in the ultimate tensile strength was observed for FSP specimens tested in chloride solution as compared to specimens tested in air. More than 75 % loss in total elongation was observed for the specimens tested in chloride solution as compared to the ones tested in air. In comparison with base material, lower time to failure was observed for processed samples. The higher SCC susceptibility of processed microstructure is attributed to increased hydrogen adsorption and favorable basal texture.