Structure and mechanical properties of unidirectionally solidified Zn-Ge eutectic alloys

The Al-Si eutectic alloys are known to undergo various structural transitions when unidirectionally solidified. This paper describes another metal/non-metal combination, Zn-Ge, which undergoes closely similar morphological changes. The tensile and compressive properties of the unidirectionally solidifed Zn-Ge eutectic have been examined and compared with those of the Al-Si eutectic. It is shown that the marked compressional stiffness of Al-Si alloys containing 〈100〉 type branched silicon dendrites only arises because of the lateral constraints of the aluminium matrix and does not occur in the Zn-Ge system.     

Ferrite structure and mechanical properties of low alloy duplex steels

It has been shown that previously unreported fine plate precipitates may be present in the ferrite phase of dual phase steels. The plates are oriented on the {100} planes and in the Fe|1.5 Si|0.15 C|0.03 Nb and Fe|1.5 Si|0.15 C|0.38 Mo alloys they significantly strengthen the ferrite phase. Based upon existing theories for precipitation strengthening, it has also been shown that there is a significant drop in the level of precipitation strengthening as the martensitic volume fraction, V_m, increases from 20% to 40%. The corresponding drop in the observed yield strength of the dual phase aggregate supports the assumption that for a martensitic volume fraction up to 40% the yield strength of this aggregate is dominated by the yield strength of the ferrite phase.Koo and Thomas (1, 2) have pointed out that the carbon content of the martensite decreases as V_m increases. It is well-established that the strength of this phase is proportional to its carbon content (22). Hence the strength of the martensite will also decrease as V_m increases. It is therefore important to take the variations of σ_m, and σ_f, with martensite volume fraction, into account when applying the law of mixtures (eqn. 1) to the ultimate tensile strength of dual phase steels.     

Effect of Si on mechanical properties of low alloy steels

Abstract

The effect of Si content on mechanical properties in 0·6C–(1·0–2·5)Si–2Ni–0·2V (wt-%) steels was investigated using tensile tests, Charpy impact tests, and microstructural examination with transmission electron microscopy. The results showed that the tempering temperatures both for the maximum yield strength and for the softening of low alloy steel shifted to higher temperatures owing to the retardation of the conversion of ? carbide to cementite within martensite laths caused by Si addition. Additionally, it was found that increasing Si content shifted the tempered martensite embrittlement temperatures upwards, owing to the retardation of the formation and growth of cementite boundaries caused by the added Si.     

The temperature-dependence of the mechanical properties of unidirectionally solidified silver-germanium eutectic

Work-hardening curves of the unidirectionally solidified silver-germanium eutectic have been determined by tensile deformation between room temperature and 615° C. The transition stress, ₀ between elastic and plastic deformation of the germanium platelets, exhibits the same temperature dependence ( ₀ exp Q/KT) over the whole temperature range. ₀ is determined, however, by two effects: the temperature-dependent critical shear stress of germanium and the lowering of the shear strength, , of the phase interfaces. Estimates of yield 14 kg mm^–2 at room temperature and <0.12 kg mm^–2 at 615° C. At low temperatures (<400° C), the composite fracture is initiated by the fracture of fibres (platelets), whereas at higher temperatures, the matrix fails first. As long as the interface shear strength is sufficiently large, the composite fracture is retarded resulting in a pronounced maximum of the fracture strain at 550° C.     

The microstructure and mechanical properties of unidirectionally solidified Al−Si alloys

Hypereutectic Al−Si alloys with minor additions of Sr were directionally solidified with a temperature gradient of 125°C cm⁻¹ in the liquid. Silicon in the range 14–17 wt%, Sr in the range 0.0–0.5 wt% and specimen traction velocities between 1 and 1500 μm sec⁻¹ were used. The relationship between hardness and traction velocity and spacing in eutectic silicon morphologies is defined and shown to be of the same form as that for yield stress. The possibility of using hardness measurements to be of the same form as that for yield stress. The possibility of using hardness measurements to indicate mechanical properties is discussed. The complex regular silicon structure makes a significant contribution to the hardness of hypereutectic alloys. This makes the relationship between hardness and traction velocity more complex adding difficulties to the use of hardness to measure mechanical properties.     

Compressive properties of the unidirectionally solidified Sb-Ge eutectic

The structure and compressive properties of the faceted/faceted Sb-Ge eutectic, unidirectionally solidified over a wide range of growth rates, have been examined and compared with those of the faceted/non-faceted Al-Si and Zn-Ge eutectics. The UCS of the Sb-Ge eutectic was found to be independent of the scale of the microstructure. It is considered that this behaviour is the result of the presence of a brittle matrix and poor matrix/second phase coherence.     

Structure and mechanical properties of high-manganese dual-phase steels

The structure and mechanical properties of 3 wt% Mn ferritic dual-phase steels were examined as a function of heat treatment. Because of the high maganese content, these alloys can be prepared easily even by a simple air cooling and they show a fine dispersion of martensite phase which leads to higher tensile strength and good ductility. The addition of a small amount of silicon gives beneficial effects: the tensile strength further increases without a significant loss of ductility.     

Structure and mechanical properties of age-hardened directionally solidified AlSiCu alloys

The structure of directionally solidified Al-Si hypoeutectic alloys are generally composed of Al-matrix and Si-reinforcing phase. The growth direction of the both phases was near 200. The strength properties of an Al-Si alloy with additions of 2 wt.% and 4 wt.% copper have been investigated. These alloys were solution treated, quenched in water and aged at 200°C. Large Al₂Cu precipitates present in D.S. samples dissolved partly, and after ageing, they precipitated as the Θ′ platelets, significantly increasing the mechanical properties of the alloys. Hardness, strength and elongation were measured in the course of ageing. The structure was investigated by means of: XSAS, X-ray phase analysis, lattice parameter measurements and scanning microscopy.     

Application of decreased hot-rolling reduction treatments for improved mechanical properties of quenched and highly-tempered low alloy structural steels

Decreased hot-rolling reduction treatments from 98% = × 50 elongation to 80% = × 5 elongation, which modify the sulphide-inclusion shape from a stringer to an ellipse, have been applied to improve the mechanical properties of quenched and highly tempered low alloy structural steels. The decreased hot-rolling reduction treatments significantly increased the transverse fracture ductility at similar strengths and uniform elongation levels independent of the type of steel. The treatments also improved the transverse Charpy U-notch (CUN) impact energy independent of the type of steel. The effect of test temperature on CUN impact energy fell into two categories; (1) the treatments significantly improved transverse CUN impact energy in temperature regions which exhibited a ductile fracture mode, (2) the improvement in the mechanical properties was reduced when the temperature decreased and a brittle fracture mode appeared. The results are briefly discussed in terms of a model involving large voids initiated at sulphide-inclusion sites and local shear bands developed between the large voids.     

Section-dependent microstructure and mechanical properties of rapidly solidified and extruded Al-20Si alloy

The microstructure and mechanical properties of rapidly solidified and extruded Al-20Si alloys were studied by a combination of optical microscopy, scanning electron microscopy, X-ray diffraction, compression testing, and wear testing. The microstructure of the extruded bars showed a homogeneous distribution of different primary Si sizes and shapes embedded in the Al matrix depending on the section considered in the extruded bar. As the section changes from diagonal through perpendicular to parallel, the compressive yield strength increased from 219 through 225 to 263 MPa, respectively. The specific wear was the lowest at all sliding speeds for the parallel section in comparison to the perpendicular and diagonal sections of the extruded bar.     

Microstructure and mechanical properties of bainitic low carbon high strength plate steels

This paper reports the results of an investigation of plates produced by the advanced thermomechanical processing (TMP) schedules, which were designed using the results of a laboratory study. There were two steel compositions that corresponded to X-80 with carbon contents 0.04 and 0.07 wt.%, respectively. The variation in microstructure, hardness, tensile properties and Charpy impact properties with TMP schedule were determined, and compared with the expected requirements for X-100 linepipe steel. The relationships between microstructure and mechanical properties were experimentally obtained and discussed.     

Structure, mechanical properties and electrical resistivity of rapidly solidified Pb-Sn-Cd and Pb-Bi-Sn-Cd alloys

A series of Pb-Sn-Cd alloys containing up to 60 wt % Bi were quenched from the melt to room temperature by melt spinning. The structure of rapidly solidified (melt spun), Pb-30 wt % Sn-10 wt % Cd, Pb-30 wt % Bi-20 wt % Sn-10 wt % Cd, and Pb-60 wt % Bi-10 wt % Sn-10 wt % Cd have been investigated by means of an X-ray diffraction technique. From X-ray analysis a crystalline metastable phase, designated (Pb-Bi) is detected. The formation of a metastable crystalline phase in the range of composition investigated causes a pronounced increase in the electrical resistivity. Desirable values of hardness and elastic constants are critically evaluated. It is also observed that the values of the Fermi energy are a few electron volts. Calculated values for the concentration of the conduction electrons, N, m_-3 of Pb -60 wt % Bi-10 wt % Sn-10 wt % Cd rapidly solidified is found to be 0.985×10₂₈ m_-3.     

Structure and mechanical properties of the annealed TZAV-30 alloy

The Ti–30Zr–5Al–3V (wt.%, TZAV-30) alloy having good mechanical properties is a potential structural material to apply in the aerospace industry. The microstructure and mechanical properties of ZTAV-30 alloy underwent various annealing heat treatments were investigated. The specimens annealed from 500 to 800 °C are composed of α and β two phases. No compound is detected in specimens annealed in that temperature range. The microstructure of annealed specimens is characterized as a typical basketweave microstructure. Three microstructural parameters, thickness of plate α phase, relative fraction of β phase and aspect ratio of α grains, were measured in those annealed specimens. As the alloy annealed in the range from 500 to 800 °C, the average thickness of plate α grains increases with the increasing annealing temperature from 500 to 700 °C but decreases while annealed at 800 °C. The fraction of retained β phase increases with annealing temperature. And the aspect ratio of plate α grains decreases firstly but increases while the annealing temperature is higher than 700 °C. As the variation of those three microstructural parameters, the strength of examined alloy varies from 1269 to 1355 MPa for tensile strength and from 1101 to 1190 MPa for yield strength, inversely, the elongation changes in the range from 12.7% to 8.4%. The strengthening and toughening mechanism of the TZAV-30 alloy with basketweave microstructure is also discussed in this paper.     

Microstructural properties and hot pressing of rapidly solidified hypoeutectic low alloy white cast iron powders

Abstract

Hypoeutectic low alloy white cast iron powders were produced using a rapid solidification technique. The morphology and microstructural properties of these powders were investigated with respect to cooling rate and particle size. The density of hot pressed compacts as a function of parameters such as hot pressing time and pressure is described. It was found that retained austenite in the form of cells or dendrites was the main constituent of the powders. At 720°C the powder particles can be hot pressed into high density compacts that have a fine cementite–ferrite microstructure. These ultrafine grained compacts exhibited good superplasticity at elevated temperatures. An elongation to failure of 300% was observed.

MST/1682     

The microstructure of unidirectionally solidified Ag-Ge eutectic alloys

Ag-Ge alloys containing 15 to 22 wt% Ge were unidirectionally solidified to investigate the growth conditions for fully eutectic growth (the coupled region) in the range of growth rate 1.4 x 10^–4 to 1.1 cm sec^–1 and at a temperature gradient of 200° C cm^–1. Primary silver was not formed in the hypereutectic Ag-Ge alloys, implying that the coupled region of Ag-Ge alloys may be different from that of the other nf-f alloy systems such as Al-Si, Fe-C, Al-Ge and Al-Fe, whose coupled regions are usually skewed towards the faceted component. It was also observed that the morphologies of primary silver, primary germanium and eutectic structure were changed with increasing growth rate. Lamellar colonies were formed prominently in the fast-grown hypereutectic alloys. As the growth rate increased the tendency for branching in massive primary germanium was so pronounced that a lamellar colony was finally formed.