Dependence of magnetic properties on atomic order in 77% Ni-14% Fe-5% Cu-4wt% Mo alloys

We have studied the effect of atomic order on the lattice parameter,a, Curie temperature,T , and the initial permeability, _i, of a series of molybdenum permalloys with varied Ni-Fe ratios and molybdenum concentrations. The ordering temperature range was between 380 and 600° C. The results of the effect of short-range order and long-range order on the lattice parameter after annealing for about 5 h between 420 and 470° C indicated a decrease of between 0.15 and 0.22 pm (0.04 to 0.06%) in the lattice parameter. No superlattice lines were detected. This may probably be due to the similarity in the atomic scattering factor of nickel and iron. It was also noted that both long-range and short-range ordering increased the Curie temperature of the ordered materials by about 1.4 to 6.6% due to the production of stronger and shorter Ni-Fe bonds. The number of Ni-Fe bonds, which controls the exchange force, was found to depend on the amount of order and molybdenum content in each material. The Curie temperature, which is a measure of the exchange force, is also an indirect means of measuring the degree of lattice ordering because the exchange integral is affected by metallurgical variables such as atomic ordering, composition, etc. Results of the isothermal annealing time on the initial permeability in the temperature range (380 to 600° C) indicated that between 380 and 460°C, maximum permeability was obtained at a critical degree of short-range ordering which is thought to correspond to a state when both the magnetostriction and anisotropy constants are close to zero. The maximum permeability was independent of ordering temperature in this range, although the time to reach this maximum decreases with increasing temperature. On annealing in the temperature range 460 to 500° C, the permeability reaches a maximum, the maximum permeability in this temperature range decreases with increasing temperature. As in the lower temperature range, the time to reach this maximum decreases with increasing temperature. Annealing between 500 and 600° C produced no maximum permeability. The permeability levelled off after an initial gradual increase. The activation energies for short-range order formation were found to be smaller (between 135 and 142 kJ mol^-1) in alloys with molybdenum concentrations above 4 wt% Mo (>2.5 at.% Mo) and higher activation energies (between 196 and 210 kJ mol^–1) in alloys with molybdenum concentrations below 4 wt% Mo (<2.5 at.% Mo) which suggests the formation of different ordered structures and mechanisms below and above 4 wt% Mo.     

Precipitation hardening of Cu-4Ti-1Cd alloy

Precipitation hardening of Cu-4Ti-1Cd alloy has been studied using hardness measurements and transmission electron microscopy. This alloy exhibited hardness of 238 Hv in solution treated (ST) condition and attained peak hardness of 318 Hv after ageing at 450°C for 40 h. Electrical conductivity of Cu-4Ti-1Cd alloy increased from 5.7 %IACS (International Annealed Copper standard) in ST condition to 8.9 %IACS on ageing at 450°C for 16 h. This alloy exhibited markedly higher yield strength (751 MPa in the peak-aged condition) compared to Cu-4.5Ti alloy but the increase in UTS due to cadmium addition was less significant. The higher yield strength of ternary alloy in peak aged condition is due to the solid solution strengthening of cadmium as well as the presence of -Cu₄Ti precipitate. On over-ageing the alloy showed a decrease in hardness as a result of formation of equilibrium precipitate, -Cu₃Ti. Optical microscopy reveals single phase with equiaxed grains in solution treated condition. A coherent, metastable phase -Cu₄Ti is responsible for high strength and hardness in peak aged condition. The over-ageing in this alloy shows the formation of cellular structure at the grain boundaries of the matrix phase.     

Recovery and recrystallization processes in binary Fe3Al based alloys

Three binary alloys of composition Fe-24Al, Fe-28Al and Fe-34Al were prepared to study the recovery, recrystallization and grain growth processes in Fe₃Al based alloys. These alloys were rolled and annealed at temperatures in the range 873 K to 1273 K for two hours. Grain size measurements were performed as a function of composition, annealing temperature and time. Transmission electron microscopy showed recovered and recrystallized grains after annealing at 873 K. The mechanisms of recovery processes was found to be by the migration of single dislocations towards each other to form linear arrays which can subsequently form square or hexagonal dislocation networks. Recrystallization can take place either by the enclosure of dislocation free regions by dislocation networks or by the preferential growth of subgrains. The composition dependence of the recovery and recrystallization processes is weak.     

S2-对高强Cu-7Ni-3Al合金在NaCl溶液中耐蚀性能的影响

实验以铜镍系耐蚀铜合金为基础,利用真空熔炼法制备得到Cu-7Ni-3Al合金,通过静态浸泡法对Cu-7Ni-3Al在不同S^2-浓度的3.5%（w） NaCl溶液中的腐蚀速率及腐蚀形态进行了研究。结果表明,通过真空熔炼法能制备出综合力学性能良好的Cu-7Ni-3Al合金。S^2-的存在促进了Cu-7Ni-3Al合金的腐蚀,Cu-7Ni-3Al合金的腐蚀速率随S^2-浓度的增大而增大,原因在于Cu-7Ni-3Al合金在S^2-环境中会形成Cu₂S,Cu₂S会使表面钝化膜变脆,并且阻止氧化膜的生成从而使腐蚀加速,因此Cu-7Ni-3Al合金在3.5% NaCl溶液中随S^2-含量的增加,耐蚀性下降。     

Cyclic hardening and softening of Al-2.9% Cu-2.2% Mg-0.6% Mn alloy

Electron microscopic research results are given for the Al-2.9% Cu-2.2% Mg-0.6% Mn alloy structure after different operating times corresponding to cyclic hardening or cyclic softening. It is shown that cyclic hardening results in precipitation of S particles and cyclic softening results in three processes: dissolution of S particles, precipitation of S particles instead of S ones and/or formation of regions free from precipitates. The main fatigue crack passes through cyclic-hardened material only and the hardening phase is merely the S particles. Relations between structure, cyclic hardening, cyclic softening and accumulated cyclic deformation are observed.     

A study of spinodal decomposition in Ni-30 at% Cu and Cu-46 at% Ni-4 at% Fe alloys using electrical resistivity measurements

The spinodal decomposition in Ni 30 at% Cu and Cu-46 at% Ni-4 at% Fe alloys has been investigated using electrical resistivity measurements. The electrical resistivity results, for ageing temperatures between 423 and 823 K, were analysed from the equation of change of electrical resistivity for spinodal decomposition in binary alloys proposed by Kolometz and Smirnov, together with the classical spinodal decomposition theory of Cahn. This analysis enabled us to obtain a plot of the amplification factor, R(), as a function of temperature. From this plot, the coherent spinodal temperatures for Ni-30 at% Cu and Cu-46 at% Ni-4 at% Fe alloys were found at 590 and 790 K, respectively, and are in good agreement with experimental and theoretical values reported by other authors.     

Phase transformation in martensite of Cu-12.4% Al

Phase transformations in a Cu-AI alloy which was in the martensitic state were examined by the use of differential thermal analysis. The influence of the speed of temperature changes on the character of the phase transformation was determined. The new sequence of phase transformations in martensite is discussed and related to the physical properties (the shape memory effect). Characteristic temperatures and heats of transformation in the alloy are also estimated.     

Directional eutectoid decomposition in Cu-11.8 wt % Al

Directional eutectoid decomposition in a Cu-11.8 wt % Al alloy at a rate of 7×10^–5 cm/sec produced eutectoid colonies several inches in length, with lamellae parallel to the temperature gradient. Average lamellar spacing was 4000 Å. Significantly faster driving speeds produced martensitic structures. The maximum rate of eutectoid decomposition and the spacing observed were in agreement with earlier data from isothermal studies.     

Precipitation hardening in Cu 1.81 wt % Be 0.28 wt % Co

The structure of the precipitation hardening alloy Cu 1.81 wt % Be 0.28 wt % Co has been studied as a function of ageing temperature and time, by transmission electron microscopy. The continuous precipitation sequence found is: supersaturated solid solution G.P. zones .The G.P. zone is an ordered platelet precipitate, which is coherent on {100} matrix planes and is nucleated in very high densities (>10²⁴ m^–3). The coherency stress fields, due to the misfit of the G.P. zone and matrix, overlap to produce a net matrix contrast along {110} 10, and give the characteristic tweed structure, which can be described by the kinematical theory of diffraction. The semi-coherent intermediate precipitate is nucleated by the G.P. zones and the transformation is characterized from the changes in the arrowhead structure produced in the electron diffraction patterns. No transformation of to the equilibrium precipitate is found for the ageing times investigated.     

Precipitation hardening owing to δ′ Al3Li in low activation Al–3 Li–12Si–3Mg alloy

Abstract

The precipitation hardening behaviour owing to ordered δ′ Al₃Li in an Al–3Li–12Si–3Mg (wt-%) based alloy was investigated during aging between room temperature and 523 K after quenching from between 723 and 823 K. The induced radioactivity level of this alloy is very low, suitable for fusion reactor structures. Effects of aging temperature, solutionising temperature, and pretreatments on precipitation hardening were examined in detail. Tensile properties were also examined in the as quenched condition as a function of testing temperature between room temperature and 673 K. Yield stress exhibited a positive temperature dependence between room temperature and 523 K and decreased abruptly above 523k with increasing test temperature. The precipitation behaviour of δ′ and the strengthening mechanisms owing to δ′ were discussed.

MST/1100     

Tensile behaviour in 30Ni-30Cu-40Mn-based alloys for a dental application

It was possible to examine the tensile behaviour in experimental 30Ni-30Cu-40Mn-based alloys which were modified by alloying additions of aluminium, indium and tin. Namely, the experimental alloys were developed on the basis of crack formation in a commercial nickel-based alloy and microstructural features in nickel-based alloys investigated. The addition was done by substituting only the manganese content (40 wt%) to 35 and 40 wt%. The results indicated that both changes of tensile strength and elongation were obtained with castability values above 94%. Comparison of tensile properties in experimental Ni-Cu-Mn-based alloys studied here showed that the addition of aluminium to the alloys was appropriate to obtain results similar to those for commercial alloys, indicating that the refining of dendrite arm spacing was obtained by aluminium addition.     

Surface hardening of Al alloys through controlled ball-milling and sintering

One of the drawbacks of aluminum and its alloys is the lack of proper heat-treatment for surface-hardening. In the present work, a new and simple method of hardening the surface of aluminum and its alloys was developed. Low-energy ball-milling using specific process control agents (PCAs) was employed, using subsequent sintering in a controlled atmosphere. The PCAs in the present work were very effective both for milling and the formation of hard nanocrystalline dispersoids during sintering. The residual oxygen in a sintering atmosphere also played an important role in the formation of AIN or Al-O-N dispersoids. Through the proper control of the processing atmosphere and PCAs, the hardness and thickness of the hardened layers could be adjusted. The results of the wear test showed that the present aluminum alloys can be effectively utilized as light-weight components with a good wear resistance. Furthermore, the present method involves a simple forming process of die-compaction and sintering.