Fabrication of in situ TiB2–TiC reinforced steel matrix composites by spark plasma sintering

Abstract

In situ TiB₂ and TiC particulates reinforced steel matrix composites have been fabricated using cheap ferrotitanium and boron carbide powders by spark plasma sintering (SPS) technique. The sintering behaviour and the formation mechanism of the composite were studied. The results show that when the composite was sintered at 1050°C for 5 min, the maximum relative density and hardness of the composite are 99·2% and 83·8 HRA respectively. The phase evolution of the composite during sintering indicates that the TiB₂ and TiC reinforcements were formed in situ as follows: first, the solid/solid interface reaction between Fe₂Ti and B₄C, resulting in the formation of a small amount of TiB₂ and TiC below 950°C; second, the solid–liquid solution precipitation reaction in the Fe–Ti–B–C system, resulting in the formation of the main TiB₂ and TiC reinforcements at ～1000°C.     

Nucleation in Zn–Al alloys grain refined with Ti

Abstract

In order to understand more fully the grain refinement of Zn–Al alloys by Ti, the α′ grains in chill cast 7 and 24% Al alloys have been studied by successive polishing and etching of microsections and by scanning electron microscopy of deeply etched specimens.

Idealized models have been deduced for these grains and it appears that lobed forms nucleate and grow preferentially in the 〈111〉 directions of the nucleus cubes. Increased supercooling causes more complex branching. When visible nuclei are absent the 24% Al alloy grains appear to have had a primitive plate-like morphology soon after nucleation.

The results are unique in the field of heterogeneous nucleation because the nuclei are relatively large and have a well-defined crystalline morphology so that their orientations relative to the early grain shapes can be easily studied.

Résumé

Afin de mieux comprendre l'action du Ti sur l'affmage des grains d'alliages Zn–Al, les grain α′ d'alliages à 7 et 24% d'Al, refroidis brusquement après coulée, ont été étuditiés par polissages et attaques successifs de microsections et par microscopie électronique à balayage d'échantil1ons attaques profondément.

Des modèles idéalisés ont été doouits pour ces grains. Il semble que les formes lobées germent et croissent d'une manière privilegiée dans les direction 〈111〉 des germes cubiques. Une surfusion plus prononcée engendre un embranchement plus complexe. Quand il n'y a pas de germes visibles, il semble que les grains de l'alliage à 24% d'Al aient eu une morphologie primitive en forme de plaques peu après la germination.

Les résultats sont uniques dans le domaine de la germination hétérogène parce que les germes sont relativement gros et possèdent une morphologie cristalline bien définie, de telle sorte que leurs orientations par rapport aux formes initiales des grains peuvent être étudiées facilement.     

Synthesis of cast graphite-containing Cu–Cr–C composites

Casting with the use of low-frequency vibrations is applied to fabricate copper-based materials containing graphite and chromium. The conditions of formation of core (graphite)–shell (chromium carbide) complexes and the influence of low-frequency mechanical activation of molten copper on them are studied.     

Characterization of Fe–C–Cr Based Hardfacing Alloys

Hardfacing is one of the adaptable methods that can build up the hard and wear resistant surface layer of different materials on the surface of substrate material. It helps them withstand wear, as well as prevent corrosion and high temperature oxidation. In the present investigation three different types of Fe–C–Cr based hardfacing electrodes with varying chemical compositions were deposited on ASTM A36 steel substrate by using manual metal arc welding (MMAW) process. ASTM A36 steel was selected as a base material after consulting with Pressure and Process Boilers, Saharanpur (India), which is a leading manufacturer of boilers. ASTM A36 steel is mostly used by this company for the production of induced draft fans. MMAW process with direct current constant current type power source was used to deposit the hardfaced layers of uniform quality. Straight polarity was used for MMAW process so that more of the arc heat should be concentrated on the electrode. The hardfaced samples were characterized using various characterization techniques and the results of the same were also outlined in the present investigation.     

On hot deformation of aluminium–silicon powder metallurgy alloys

Abstract

The growing field of aluminium powder metallurgy (PM) brings promise to an economical and environmental demand for the production of high strength, light weight aluminium engine components. In an effort to further enhance the mechanical properties of these alloys, the effects of hot upset forging sintered compacts were studied. This article details findings on the hot compression response of these alloys, modelling of this flow behaviour, and its effects on final density and microstructure. Two aluminium–silicon based PM alloys were used for comparison. One alloy was a hypereutectic blend known as Alumix-231 (Al–15Si–2·5Cu–0·5Mg) and the second was an experimental hypoeutectic system (Al–6Si–4·5Cu–0·5Mg). Using a Gleeble 1500D thermomechanical simulator, sintered cylinders of the alloys were upset forged at various temperatures and strain rates, and the resulting stress–strain trends were studied. The constitutive equations of hot deformation were used to model peak flow stresses for each alloy when forged between 360 and 480°C, using strain rates of 0·005–5·0 s^?1. Both alloys benefited from hot deformation within the ranges studied. The experimental alloy achieved an average density of 99·6% (±0·2%) while the commercial alloy achieved 98·3% (±0·6%) of its theoretical density. It was found that the experimentally obtained peak flow stresses for each material studied could be very closely approximated using the semi-empirical Zener–Hollomon models.     

Production of NiAl–matrix composites by reactive sintering

Abstract

This work was devoted to the development of NiAl–matrix composite and its production by reactive sintering powder metallurgy. Various types of reinforcement (aluminium oxide, silicon and tungsten carbides, titanium silicide) were tested. The best chemical compatibility and the highest hardness and wear resistance were achieved by Al₂O₃ fibres. Electroless nickel plating pretreatment of Al₂O₃ fibres improves both distribution of fibres and hardness of the composite. However, it strongly reduces the wear resistance, probably due to phosphorus content in the nickel coating. In situ formation of NiAl–Al₂O₃ composites by reactive sintering of a pressed powder mixture of Ni, Al and NiO was unsuccessful. Only a small amount of cubic γ-Al₂O₃ was detected after reactive sintering and hence no significant hardness increase was observed.     

Synthesis of TiC–TiB–TiB2 composite powders by solid reaction of powders

In the present work, TiC–TiB–TiB₂ diffusion-layer-coated B₄C composite powders were synthesised via a powder immersion method using Ti and B₄C powders as reactants. The phase compositions and microstructure of the treated powders were characterised by employing X-ray diffraction and scanning electron microscopy. No significant reaction between B₄C and Ti could be detected at 800°C. After treatment at 900°C, the products generated were composed of TiC and TiB. After treatment at 1000°C, the products generated were primarily composed of TiC and TiB, with a small amount of TiB₂. The composition and proportions of the produced phases varied with process temperatures and the composition of the initial powders used. Powder mixtures with a Ti/B₄C molar ratio of 3.5:1 and treated at 1000°C for 14?h were more suitable for synthesis of TiC–TiB–TiB₂-coated B₄C composite powders.     

Synthesis and Spectroscopic Characterization of Compounds of Lanthanide-2,4-Pentanedionates with Pyridine

Compounds of the formula [Ln(pd)_3(py)_2] where Ln=La～Yb and Y except Pm and Tin,Hpd (=2,4-pentanedione) and py (=pyridine) have been synthesised and characterised by physical and spectral studies.Pyridine is coordinated in all the compounds.The covalency parameters β,b~(1/2),δ and η indicate at least somecovalency in these compounds.The compounds have been checked for their use as NMR shift reagents usingcholesterol as substrate.Eight coordinate compounds increase their coordination number when added to thesubstrate.     

Structural heterogeneity and its effects on the properties of an in situ TiB2–TiC/Cu composite synthesised by hot pressing

ABSTRACT

In situ TiB₂ and TiC reinforced copper matrix composites with tailored heterogeneous structure were fabricated via high-energy ball milling of Cu, TiH₂ and B₄C powders followed by hot pressing. The microstructures of both ball-milled powders and hot-pressed composites were compared. Although the dislocation density of Cu matrix was changed after hot pressing, the mode of distribution of ceramic phases in the Cu matrix was noted to transmit from the ball-milled powders to hot-pressed composites in case of the TiH₂ particles synthesised by the in situ reactions. The structural inheritance between the ball-milled powders and hot-pressed composites could be used to control microstructural features and thus to tune properties. The hot-pressed TiB₂–TiC/Cu composites with tailored heterogeneous structure exhibited better performance than those of homogeneous counterparts.     

Self-Propagating High-Temperature Synthesis of (Al–2% Mn)–10% TiC and (Al–5% Cu–2% Mn)–10% TiC Nanostructured Composite Alloys Doped with Manganese Powder

Russian Journal of Non-Ferrous Metals - The influence of alloying with powder manganese on the preparation of nanostructured (Al‒2% Mn)–10% TiC and (Al–5% Cu–2%...     

An exemplar-retrieval model of speeded same–different judgments.

R. M. Nosofsky and T. J. Palmeri's (1997) exemplar-based random-walk (EBRW) model of speeded classification is extended to account for speeded same–different judgments among integral-dimension stimuli. According to the model, an important component process of same–different judgments is that people store individual examples of experienced same and different pairs of objects in memory. These exemplar pairs are retrieved from memory on the basis of how similar they are to a currently presented pair of objects. The retrieved pairs drive a random-walk process for making same–different decisions. The EBRW predicts correctly that same responses are faster for objects lying in isolated than in dense regions of similarity space. The model also predicts correctly effects of same-identity versus same-category instructions and is sensitive to observers' past experiences with specific same and different pairs of objects. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Comparative Study of Coatings formed by Electrospark Alloying Using TiC–NiCr and TiC–NiCr– Eu2O3 Electrodes

Russian Journal of Non-Ferrous Metals - Coatings formed on steel 40Kh by electrospark alloying (ESA) using TiC–NiCr and TiC–NiCr–Eu2O3 electrodes are investigated. The coatings...     

Properties of a 45Ti–45Ni–10Nb shape memory alloy in the as-cast and pressed states

The structural and functional properties of specimens cut from as-cast and pressed rods of a 45Ti–45Ni–10Nb (at %) alloy have been studied in as-delivered state. The homogeneity of the properties under study has been verified along the rod length and from rod to rod. The laws of formation of the alloy structure as a function of the technology of its manufacturing have been studied. The structure influences the mechanical behavior and the main functional properties of the alloy. The pressed state is shown to be preferable as compared to the as-cast state.     

Synthesis and Characterization of Lanthanum Complexes with Amino Acid Schiff Base

Ｉｎｔｈｅｌｉｖｉｎｇｂｅｉｎｇｓ ,ｃａｌｃｉｕｍｉｏｎｐｏｓｓｅｓｓ ｅｓｍａｎｙｋｉｎｄｓｏｆｉｍｐｏｒｔａｎｔｂｉｏｌｏｇｉｃａｌｆｕｎｃｔｉｏｎ .Ｔｈｅｒａｄｉｕｓａｎｄｔｈｅｃｏｏｒｄｉｎａｔｅａｃｔｉｏｎｏｆｌａｎ ｔｈａｎｕｍｉｏｎａｒｅｓｉｍｉｌａｒｔｏｔｈａｔｏｆｃａｌｃｉｕｍｉｏｎ .Ｃｏｎｓｅｑｕｅｎｔｌｙ ,ｌａｎｔｈａｎｕｍｉｏｎ ,ｗｈｉｃｈｅｎｔｅｒｓｔｈｅｂｏｄｙ ,ｗｉｌｌｒｅｐｌａｃｅｃａｌｃｉｕｍｉｏｎａｎｄｓｈｏｗａｓｅｒｉｅｓｏｆｂｉｏｌｏｇｉｃａｌｅｆｆｅｃｔｓ…     

Characterization of Alumina–Molybdenum Composites Prepared by Gel Casting Method

Powder Metallurgy and Metal Ceramics - This work concerns the study of ceramic-metal composite materials processed by gel casting method. Due to limited possibilities of fabrication complex-shape...     

Effect of Particle Size on the Deformation Behaviour of Sintered Al–TiC Nano Composites

Cold upsetting experiment was impeccably carried out on sintered Al–TiC preform to evaluate their deformation characterization. Effects of TiC content and aspect ratio of the preform on deformation behaviour were completely investigated by using Zinc stearate as a lubricant. Cylindrical preforms with different particle size at 5% (2 μm and ≤200 nm) and different aspect ratios (1.00 and 0.75) were prepared by using suitable die, on a 1.0 MN capacity hydraulic press and sintered in electrical muffle furnace for 1.5 h and followed by cooling the furnace to its room temperature itself. Analysis of the experimental data have proved the power law relationship between fractional theoretical density \(\left( {\frac{{\rho_{f} }}{{\rho_{th} }}} \right)\) and strain factor \(e^{{(\varepsilon_{z} - \varepsilon_{\theta } )}}\). Further, it was found that the preforms with low size of TiC content showed higher value of deformation properties such as axial stress and the Poisson’s ratio than high size of TiC preform, provided that the initial fractional density taken was kept constant.     

Characterization of Tantalum–Titanium Powders with Universal Powder Bed (UPB) System for Electron Beam Melting Process

Russian Journal of Non-Ferrous Metals - Electron beam melting (EBM) is a powder bed fusion additive manufacturing (AM) technique that produces three-dimensional (3D) parts by fusing metallic...     

Synthesis and Characterization of Ti/(TiB + TiC) Hybrid in-situ Composites by Spark Plasma Sintering

Since Ti alloys exhibit inferior wear resistance and suffer considerable loss in mechanical strength at high temperature, it is aimed at synthesis an in-situ Ti/(TiB + TiC) hybrid composite. In order to synthesis Ti/(TiB + TiC) in-situ composite, B₄C particulate was mixed with titanium powder and sintered at 1400 °C at different time intervals by spark plasma sintering. Sintering parameters were optimized according to the complete in-situ reactions. Density of the sintered compacts was measured by Archimedes principle. Energy dispersive spectroscope and optical microscope observations of the sintered samples revealed that with increasing sintering time TiB and TiC particulates were gradually transforming into needle like structure and near equiaxed structure, respectively.     

Characterization of Structure–Property Relationship of Incoloy 825 and SAF 2507 Dissimilar Welds

This study was carried out to investigate the evaluation of dissimilar welding between Incoloy 825 Ni-based alloy and SAF 2507 super duplex stainless steel. Welding was conducted by pulsed current (PC) and continuous current (CC) gas tungsten arc welding (GTAW) methods using ERNiCrMo-3 filler wire. The microstructure of weld zones and base metal/weld interfaces as well as mechanical properties of weldments were characterized. The results detailed the formation of Nb, and Mo-rich phases in the inter-dendritic regions of weld metals leading to a decrease in impact resistance of weld zones in comparison to parent metals. Presence of more secondary phases at the CCGTA weld metal resulted in higher hardness and lower toughness than that of the PCGTAW sample. During tensile tests, fracture occurred at the Incoloy 825 base metal, and both weldments also underwent ductile mode of fracture. The research addressed the microstructure–property relationship for dissimilar weld joints.