The ageing characteristics of an Fe-19 wt% Ni-9 wt% Co-5 wt% W alloy

In the present paper, we compare the behaviour during ageing in the temperature range 380 to 530° C of the two martensitic alloys Fe-18.65 Ni-8.99 Co-4.87 Mo and Fe-18.65 Ni-8.99 Co-4.87 W (wt %). The kinetics of precipitation were followed by measurements of hardness, by resistometric measurements and electron microscopy. In the case of the alloy with Mo, Mo at first concentrates in local clusters, then an phase is formed, and above 450° C, finally a Ni₃Mo or Laves phase (Fe, Ni, Co)₂ Mo is formed. In the case of the alloy with W, phase formation was not observed but an intermetallic precipitate isomorphous with Ni₃Mo, (Fe, Ni, Co)₃ W = A₃W was found. The precipitates are rod-shaped, of several nm in length. The preferred direction of growth of these precipitates is 1 1 1 of the martensitic matrix and the orientation relationship with the martensitic matrix is (0 1 1)_M (0 1 0)A₃W and [1 1 1]_M [1 0 0]A₃W, identical to that found for the Ni₃Mo precipitate in the (Fe, Ni, Co, Mo, Ti) industrial maraging steel.     

On the formation of a microduplex structure in a Cu-15 wt% Ni-37.5 wt% Zn alloy

Interaction of recrystallization and precipitation during annealing of a cold-worked supersaturated solid solution can lead to the formation of an ultrafine grain size, two-phase microstructure, termed microduplex. In Cu-15 wt % Ni-37.5 wt % Zn this process requires prior cold-work of more than 60% RA. Cell walls and subgrain boundaries introduced by the deformation act as preferred nucleation sites for second phase particles. A high density of small particles is formed before recrystallization can start. Recrystallization then becomes controlled by the coarsening of the particles. A microstructure with grains and particles of less than 1 μm diameter results.     

Microstructural evolution of annealed Al–5 wt% Ca–5 wt% Zn sheet alloy

Microstructural evolution on annealing of Al–5 wt% Ca–5 wt% Zn sheet alloy has been systematically investigated by means of texture analysis and optical and transmission electron microscopy. Heat treatments in the temperature range of 100 to 540 °C for times between 0.11 (7 min) and 90.5 h have been performed. After annealing, the main texture component of the as- received material, {1 1 3} <3 3 2>, was retained, whereas the minor components, {0 1 3} <3 1 0> and {0 1 1} <1 0 0>, showed clear changes depending on the annealing conditions. Additional minor components appeared upon heat treatments. Continuous recrystallization, subgrain accommodation by means of rotation and subsequent extensive grain growth are the processes which account for all the microstructural changes observed. This revised version was published online in November 2006 with corrections to the Cover Date.     

Microstructural modification during isothermal ageing of a low nickel duplex stainless steel

In order to reduce the cost of duplex stainless steel (DSS), the Ni could be partially substituted by Mn and N, to maintain the alpha/gamma microstructure, the corrosion resistance and mechanical strength similar to the common Ni–Cr–Mo DSS. In this paper the microstructure stability, impact strength and the general corrosion behaviour of a low Ni grade, 22Cr–4Mn–0,2N DSS, were examined. In the solution annealing condition the corrosion resistance is quite similar to the austenitic grade. A moderate precipitation of nitrides and carbides was evidenced after isothermal treatment in the range 600–900 °C, while no dangerous topologically close packed phases (TCP-phases) were detected. The precipitation affects the impact strength, which decreases to about 50 J, while the corrosion resistance is less markedly affected.     

Microstructural characterization of a rapidly-solidified Al-12 wt% Si alloy

Optical, electron metallography and X-ray diffraction techniques were employed to characterize the microstructure of a rapidly solidified Al-12 wt% Si alloy. Ribbons produced with the planar flow casting process at a cooling rate of 10⁶ Ks^–1, had a very fine cellular structure of Al and nanosize Si particles which are distributed inside and at the boundaries of these cells. Thinner sections (t<30 m) have apparently experienced higher cooling rates and show, in addition to a cellular structure, a distinct zone which is featureless at optical microscope magnifications.     

Microstructural changes of Pt/Ti bilayer during annealing in different atmospheres — an XRD study

The high temperature behaviour of Pt/Ti base electrode bilayers is crucial for the deposition of ferro-electric thin films on top of such metal films. Therefore the microstructural development during annealing has to be considered. These parameters are studied by X-ray diffraction (XRD). Comparing the microstructure before and after thermal treatment significant differences could be found. Pt₃Ti compound formation was observed in all coatings. The stress in the Pt phase changes from compressive to tensile during annealing. In contradiction the stress in the Pt₃Ti phase is compressive after thermal treatment. From measurements of the total reflected signal an amount of TiO₂ on the surface of the oxygen treated film could be found. A model based on diffusion of Ti along grain boundaries and considering thermodynamic aspects of stress development is predicted to describe the microstructural changes during annealing.     

Thermal conductivity of Cu-4.5 Ti alloy

The thermal conductivity (TC) of peak aged Cu-4.5 wt% Ti alloy was measured at different temperatures and studied its variation with temperature. It was found that TC increased with increasing temperature. Phonon and electronic components of thermal conductivity were computed from the results. The alloy exhibits an electronic thermal conductivity of 46.45 W/m.K at room temperature. The phonon thermal conductivity decreased with increasing temperature from 17.6 at 0 K to 1.75 W/m.K at 298 K, which agrees with literature that the phonon component of thermal conductivity is insignificant at room temperature.     

机械球磨Cu-15%Cr复合粉末的致密化工艺研究

探讨机械球磨Cu—15％Cr复合粉末经真空烧结后采用热静液挤压致密化的可能性．研究了机械球磨时间、烧结温度、保温时间和挤压温度等工艺参数对材料致密化的影响．结果表明,热静液挤压工艺可以有效的促进机械球磨复合粉末的致密,所获得的材料具有优异的组织性能．     

Mechanical properties and fracture characteristics of aged Cu-1.8 wt% Be-0.2 wt% Co alloy in various loading modes

The fracture of a Cu-Be alloy was examined in various loading modes. For the tensile mode, two degrees of ageing were also tested. The common fracture mode was defined as a dimpled intergranular, and its relation to the precipitate morphology is discussed.     

Lattice changes in the martensitic phase due to ageing in 18 wt% nickel maraging steel grade 350

Changes in the lattice parameter of martensite phase in a maraging steel is measured as a function of ageing temperatures. A decrease in the lattice parameter is observed when aged between 400–650°C which is attributed to the depletion of alloying elements in the martensite matrix as a consequence of precipitation and austenite formation. An increase in the lattice from 650 to 710°C was characteristic of enrichment of alloying elements in the martensite matrix due to dissolution of austenite phase. A minimum value of the lattice parameter of martensite is observed at 650 °C which coincides with the maximum vol % of retained austenite. Electrical resistivity, hardness measurements, andin situ high temperature dilatometry was also carried out to delineate various precipitation reactions that occur in this steel.[/p]     

Reverse martensitic transformation in the Cu-10 wt% Al-6 wt%Ag alloy

The reverse martensitic transformation in the Cu-10 wt%Al-6 wt%Ag alloy was studied by classical differential thermal analysis (DTA), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX) and X-ray diffractometry (XRD). The results indicated that the presence of Ag in the Cu-10%Al alloy is responsible for the separation of the competitive reactions that occur during the reverse martensitic transformation and is also associated to an increase in the disordering degree at high temperatures, when compared with alloys without Ag addition.     

定向凝固Cu-Cr自生复合材料的微观组织演变

为了研究定向凝固Cu-Cr自生复合材料的微观组织构成及其在不同凝固速度条件下的组织演变,在高梯度定向凝固装置上制备了Cu-1.0%Cr、Cu-1.7%Cr(质量分数)两种成分的Cu基自生复合材料,采用金相显微镜、扫描电镜以及能谱分析进行了微观组织观察和相的成分分析.研究表明:Cu-1.0%Cr亚共晶合金定向凝固组织为初生α相和棒状(或针状)共晶体(α β)的混合组织;Cu-1.7%Cr过共晶合金为α相、初生β相和共晶(α β)的混合组织;随着凝固速度的提高,α相一次胞(枝)晶逐渐细化,晶间距逐渐减小;共晶体(α β)分布在α相胞(枝)晶间,起到强化基体的作用;初生β相呈颗粒状不均匀地分布在α相基体上.