The effects of MgO and Al2O3 behaviours on softening–melting properties of high basicity sinter

Because the behaviours of MgO and Al₂O₃ during slag formation of high basicity sinter are not clearly understood, the effects of MgO and Al₂O₃ on softening-melting properties are always arguable. In this paper, four kinds of sinter containing different MgO and Al₂O₃ content are investigated. Some observations are obtained. The mechanism of the influence of MgO and Al₂O₃ on softening properties of sinter are different. Al₂O₃ has priority over MgO to enter into slag phase and forms low-melting point phase while MgO remains unslagged state and mainly exists in wustite as FeO–MgO solid solution. When sinter melts, the viscosity of the slag generated from sinter containing high MgO and Al₂O₃ content is low, which could result in low pressure drop. As MgO and Al₂O₃ content increase, the main minerals of residual slag change from 2CaO?SiO₂ to merwinte and melilite. The changes of the minerals in slag phase can well explain the trend of softening-melting characteristic temperatures.     

Influence of the solidification temperature–time parameters on the structure and mechanical properties of nickel aluminide–based alloys

The influence of the technological parameters of directional solidification, namely, the solidification rate and the temperature gradient, on the microstructure, the structure–phase parameters, and the mechanical properties of nickel aluminide–based intermetallic alloys is considered.     

A study on mathematical simulation of spray forming process

An integrated approach for modeling the entire spray forming process is presented in this paper, and the program for the simulation is developed. The whole spray forming process can be divided into four calculation processes and the basis for the analysis is the classical k -ε turbulence model which was used to simulate the flow field of gas formed in the chamber. In the atomization model the flow field of gas is coupled with formation, velocity and location of droplet. By means of the above mathematical model, the process of spray forming was simulated.     

Effect of composition of starting materials of Mo–Si on self-propagating high temperature SHS reaction

Abstract

An experimental study of the self-propagating high temperature synthesis of Mo–Si alloys was conducted from elemental powder compacts. Test specimens with seven compositions, including Mo/Si?=?1∶1·25, 1∶1·50, 1∶1·75, 1∶2·00, 1∶2·25, 1∶2·50 and 1∶2·75 respectively, were employed. Experimental evidence showed that a combustion wave featuring a spinning reaction zone can be observed. When the powder compacts are from Mo∶1·25Si to Mo∶1·75Si, the combustion temperature and the propagation velocity of combustion wave increase with increasing silicon in the sample, and the combustion products are composed of MoSi₂, Mo₅Si₃ and Mo. However, when the powder compacts are from Mo∶2·25Si to Mo∶2·75Si, the combustion temperature and the propagation velocity decrease rapidly as the silicon in the compact increases, and the combustion products are composed of MoSi₂ and Si. The sample with Mo/Si?=?1∶2·00 possesses the highest combustion temperature (1628·9 K) and propagation velocity (3·13 mm s^?1). A single-phase MoSi₂ is synthesised by the Mo/Si?=?1∶2·00 sample.     

Dispersoid additions and their effect on high temperature deformation of FeAl

Small additions of carbon and ZrB₂ have been introduced into an FeAl alloy in order to obtain homogeneous distributions of different dispersoid particles in the B2 matrix. The carbon additions have produced the formation of second phase particles with a complex cubic structure (perovskite). The influence of these particles on the room and high temperature yield strength of the intermetallic has been compared to that of the ZrB₂ particles. Tensile tests of these alloys have been performed between 25°C both types of particles produced a substantial increase, only the ZrB₂ particles retain much of this strength at 600°C. The much faster decrease of stregth with temperature observed in the carbon containing alloy is explained in terms of a deformation process where the perovskite particles constitute a composites material with the matrix deforming at different rates.     

Parametric optimization of EDM process on α–β brass using Taguchi approach

In the present work, stir casting route is used to fabricate the duplex (α–β) brass plate. The machineabilty behavior of the (α–β) brass is analyzed during Electrical Discharge Machining (EDM) using Taguchi method. Experiments were conducted with three machining variables such as current, pulse-on time and voltage. Material removal rates (MRR), Electrode wear rate (EWR) and surface roughness (SR) are chosen as the output parameters. Results of SN ratio analysis showed that peak current was significant factor to affect the all the responses. Analysis of variance (ANOVA) was used to identify the contribution of each parameter.     

Effect of the temperature–rate parameters of directional solidification on the structure formation in high-temperature materials

The effect of the temperature gradient and the crystal growth rate on the structure formation in nickel and niobium superalloys is studied under the conditions of the flat, cellular, dendritic, or dendritic–cellular configuration of a solidification front during directional solidification.     

Water–air online quenching process of 3Cr2Mo steel based on numerical simulation

A three-dimensional finite element model was established to investigate the water–air online quenching process of 3Cr2Mo steel with 130-mm thickness. The temperature, metallographic structure and stress–strain fields of the steel were calculated under single-pass continuous quenching, multi-pass continuous quenching and multi-pass interrupted quenching (MPIQ) processes. The results show that the three quenching processes can avoid the pearlite appearance, and MPIQ process could be more effective to decrease the brittleness of steel. Besides, MPIQ process is able to reduce stress–strain, minimise deformation and avoid cracking problem. The hardness and the metallographic structure were tested after MPIQ process and tempering. After tempering, the metallographic structures were all tempered sorbite, and the hardness difference of the whole steel was less than 3HRC with no cracks. It can draw the conclusion that the MPIQ process is a suitable quenching process for 3Cr2Mo steel.     

On development of press and sinter Al–Ni–Mg powder metallurgy alloys

Abstract

The objective of this research was to initiate the development of powder metallurgy alloys based on the Al–Ni–Mg system. In doing so, binary (Al–Mg) and ternary (Al–Ni–Mg) blends were prepared, compacted and sintered using elemental and master alloy feedstock powders. Research began with fundamental studies on the sintering response of the base aluminium powder with additions of magnesium. This element proved essential to the development of a well sintered microstructure while promoting the formation of a small nodular phase that appeared to be AlN. In Al–Ni–Mg systems a well sintered structure comprised of α aluminium plus NiAl₃ was produced at the higher sintering temperatures investigated. Of these ternary alloys studied, Al–15Ni–1Mg exhibited mechanical properties that were comparable with existing commercial 'press and sinter' alloys. The processing, reaction sintering and tensile properties of this alloy were also found to be reproducible in an industrial production environment.     

Effect of the sintering temperature and time on the structure and phase composition of temperature stable hard magnetic materials of the REM–Fe–Co–B system

The structure, the phase composition, and the distribution of alloying elements in the structure of temperature stable hard magnetic materials of the REM–Fe–Co–B system (REM = rare-earth metals), which are prepared under different manufacturing conditions, namely, at different sintering temperatures and times, have been studied. The phase composition, the local chemical composition of phases, the volume fraction of pores, and the manufacturing conditions that allow one to prepare the structure ensuring high magnetic properties have been determined.     

Effect of chilling and cerium addition on microstructure and cooling curve parameters of Al–14%Si alloy

Abstract

Al–14%Si alloys, with and without cerium, were cast at varying cooling rates by solidifying them in a crucible and against chills. The effect of melt treatment and chilling on microstructure and cooling curve parameters of the alloy was assessed. Ce treated alloys solidified in clay graphite crucible at a slow cooling rate showed refinement of primary silicon and the formation of Al–Si–Ce ternary intermetallic compound. The addition of Ce to the alloy solidified against chills resulted in simultaneous refinement and modification of primary and eutectic silicon. Nucleation temperatures of both primary and eutectic silicon decreased on addition of cerium. The formation of the intermetallic compound decreased with increase in cooling rate, leading to the modification of the eutectic silicon. The increase in the degree of modification of the eutectic Si was associated with the decrease in the volume fraction of the intermetallic compound formed.     

Influence of process conditions during Ruhrstahl–Hereaeus refining process and effect of vacuum degassing on carbon removal to ultra-low levels

Abstract

The effect of the time taken to add the alloy and the gas injection mode are significant factors for fast decarburisation. Industrial experiments and thermodynamic calculations are adopted to show the transition of the main factors and reaction sites with time. The results indicate that adding steel scrap and alloy are not recommended in the first 7 min in order to keep good thermodynamic and dynamic conditions. The gas injection mode is more critical for reducing the chamber pressure to 67 Pa in 8.5 min and the gas volume should be less than 10 m³ in the first 4 min after the reaction begins. This method is effective in improving the decarburisation rate and decreasing the carbon content at the end of decarburisation. For 69% of the site tests the final carbon content was kept to about 10 ppm within 15 min.     

Processing and properties of sinter hardened Fe–Cr–Mo steels with admixed extra-fine nickel

Abstract

The processing and properties of chromium–molybdenum, powder metallurgy steels with admixed extra-fine nickel (XF Ni) were investigated. Prealloyed Fe–1·5Cr–0·2Mo powder was blended with different quantities of XF Ni, while a hybrid steel with lower Cr content was prepared by blending Fe–1·5Cr–0·2Mo and Fe–0·5Mo prealloyed powders, with additions of XF Ni and copper powders. These steels were compacted into different part shapes in order to evaluate the effect of part thickness on sinterhardening behaviour. These parts were also subjected to different cooling rates after sintering. This study showed that additions of XF Ni improve the compressibility, densification behaviour and mechanical properties of Cr–Mo steels. Furthermore, the properties of the hybrid steel were shown to be either equal to or greater than those of the reference material. Hardenability of all steels was sufficiently high such that part thickness was seen to have negligible impact. Higher cooling rates generally resulted in improved mechanical properties.     

The role of solution heat treatment on corrosion and mechanical behaviour of Mg–Zn biodegradable alloys

The mechanical properties and bio-corrosion behaviours of T4 solid solution heat-treated Mg–1.5Zn and Mg–9Zn alloys at 340°C under different heat treatment durations were investigated. In vitro corrosion behaviour of the heat-treated alloys immersed in simulated body fluid (SBF) were measured by electrochemical, hydrogen evolution and mass loss tests. Surface examination and analytical studies were carried out using optical and scanning electron microscopy, EDX, and X-ray diffractometry. The results show that the grains size of both the alloys apparently remained unchanged after T4 treatment. T4 treatment at 340°C for 6?h slightly increased the strength and elongation of Mg–1.5Zn alloy while it significantly improved the strength and elongation of the Mg–9Zn alloy because of the presence of residual Mg₅₁Zn₂₀ and Mg₁₂Zn₁₃ secondary phase at the grain boundary. The results of electrochemical tests show that the corrosion rate of both the alloys decrease with increasing treatment temperature. The result also shows corrosion resistance of both the T4 tread alloys much better than that of as-cast samples. The corrosion mechanism exhibited that the occurrence of galvanic and pitting corrosion, which varied with the alloy composition and treatment time.     

Effect of cyclic stress on the high temperature creep behavior of AlMg alloys

The effect of cyclic stress on high temperature creep and also the dislocation structures developed during cyclic creep for three AlMg solid solutions have been studied. When the steady state creep rate is the range of 10⁻⁸ s⁻¹, cyclic creep with complete unloading (R = 0) exhibited only the transition from class M to class A creep instead of the two transitions from class M to class A and then to class M again ihe corresponding static creep. The threshold stress for the transition in cyclic creep was found to be close to or larger than that for the class A to class M transition in the static creep. With increase in magnesium content, cyclic creep retardation became stronger at lower stresses. However the transition from retardation to acceleration in the cyclic creep has been observed at higher stress levels only in the high magnesium alloys. Also found were two types of relationships between the unloading amount and steady state creep rate. The micromechanisms of cyclic creep, especially the interaction of dislocations with solute atoms, have also been discussed.     

Effect of heat treatment on the dispersity of Sn(IV)—Sb—O powders and the porosity of thick-film gas sensors based on them

A study is made of how the granulometric composition and porosity of powders of solid solutions in the system Sn(IV)−Sb−O is affected by the conditions of precipitation of mixtures of tin hydroxide and antimony hydroxide and the heat-treatment temperature. Powders of tin and antimony hydroxides have a microporous structure and a high (≥200 m ²/g) specific surface. Heat treatment above 870 K forms Sn_1−xSb_xO₂ solid solutions, this being accompanied by an increase in the size of the particles and transformation of the microporous structure to a mesoporous structure. An increase in the antimony content of the solid solutions helps form finer powders. A examination is made of the parameters of the pore structure of bulk specimens of semiconductor gas sensors obtained by heat-treating mixtures of powders of solid solutions and ultrafine clay. Institute for Problems of Materials Science, Ukraine National Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurgiya, Nos. 5–6(407), pp. 111–116, May–June, 1999.     

Investigation of deformation and heat treatment effects on properties of PM 92.5W–5Ni–2.5Fe heavy alloys

Abstract

This paper presents the effects of vacuum heat treatment under different cooling conditions on mechanical and structural properties of forged heavy alloys, such as 92.5W–5Ni–2.5Fe and 92.5W–5Ni–25Fe microalloyed with Co. The tungsten composition in the c phase has proved to be higher and more homogenous in the rapidly cooled alloys than in the slowly cooled ones. The effects of chemical composition inhomogeneity on mechanical and structural properties of alloys were also analysed and discussed. The results of tensile and toughness testing have shown an increase in ductility and toughness, while the strength of heat treated alloys decreased in comparison with the strength of forged alloys. The fracture analysis has shown that in the sintered and rotary forged alloys, intergranular fracture of the tungsten phase and transgranular fracture of the γ phase occurred, respectively. The fracture of these phases after heat treatment was characterised by transgranular morphology.