Advanced Materials Research Vols. 89-91

Abstract: The present paper focuses on the influence of combined additions of Zr and Mn on the recrystallisation resistance of aluminium alloy 2198 sheet. Dual additions of these dispersoid forming elements have previously been reported to be beneficial for reducing recrystallisation during solution treatment, as they exhibit opposing microsegregation partitioning on solidification. Contrary to expectation, it was found that the addition of Mn, to a standard Zr-containing 2198 sheet material, reduced recrystallisation resistance. The reasons for this behaviour are explored by analysis of the morphology, size, chemistry, and distribution of the dispersoid families formed, as a function of the Mn and Zr level, traced back to the homogenisation stage.

Abstract: Phase equilibrium and phase constitution of the Au-Cu-Ga-Mn quaternary system at 873 K was studied along the AuMn-Cu2MnGa (=CuMn0.5Ga0.5) both of which are ferromagnetic shape memory alloys. Three alloys were investigated: AuMn, Cu2MnGa and Au0.5Cu0.5Mn0.75Ga0.25 (AuMn:CuMn0.5Ga0.5=1:1). It was found that 1 ordered bct phase with the axis ratio c/a=0.948 was formed in the AuMn alloy due to the Mn reduction by evaporation during melting. The CuMn0.5Mn0.5 alloy was composed of MgZn2-type Laves phase and Cu9Al4-type  phase. Besides, the following three phases existed in the Au0.5Cu0.5M0.75Ga0.25 alloy: Laves,  and 2 ordered bct with c/a=1.041. The c/a value of the ordered bct phase is decreased by Cu and/or Ga substitution in AuMn. The values of electron atom ratio (e/a) calculated based on chemical compositions for the  phases were 1.61 and 1.68, which were close to the ideal value of 1.62 (=21/13). Based on the results, ordered bcc  (transforming into bct at lower temperature), and Laves are judged to be equilibrium phases at 873 K along the AuMn-Cu2MnGa.

Abstract: The microstructural control of rolled products is based on managing the austenite phase transformations during and after hot deformation to attain the desired microstructure after the cooling step. Therefore, it is very important an appropriate description of the kinetics of the hardening and softening phenomena taking place during the deformation at high temperatures, namely, dynamic recovery (DRV) and recrystallization (DRX). This investigation examines the effect of manganese contents on the hot flow behaviour of plain carbon steels. For this purpose, uniaxial hot compression tests were carried out in carbon steels in an extensive range of temperatures, from 1123 to 1373 K and strain rates, from 510-4 to 110-1 s-1. This work is focused in determining the physically-based constitutive equations that govern the plastic behaviour of plain carbon steels. Experimental results were compared with the predictions of the model and an excellent agreement over a broad range of temperatures and strain rates was obtained.

Abstract: A Ti-47Al-2Cr-2Nb (at.%) material was fabricated using two laser-based methods, “Selective Laser Melting” (SLM) and “Direct Metal Deposition” (DMD), for potential uses in aircraft jet engines. Experiments were conducted under controlled atmosphere by changing the processing parameters. Optimal parameters were searched for this relatively low ductility material to prevent cracking due to built-up residual stresses during fast cooling. It was observed that these non-equilibrium cooling conditions were fast enough to generate ultra fine and metastable structures exhibiting high microhardness values. Post heat-treatments were successfully used to restore homogeneous lamellar or duplex microstructures and to relieve the residual stresses. A comparison of these two methods is provided in terms of powder requirements and of process parameters to achieve noncracked structures and fully dense materials.

Abstract: The recrystallization behaviour of near-alpha titanium alloy IMI834, which is primarily used for high temperature aerospace compressor disc applications, has been investigated at hot working temperatures. The latest results of a finite element model, developed using the commercial code DEFORM-3D with constitutive equations adapted from available literature, will be presented. Model development and validation involved the hot compression of specimens with an initial bimodal alpha+beta microstructure at temperatures of 1000°C-1100°C, strain rates of 0.01s 1-1s 1, and varied post-deformation annealing times. The characterization of microstructure through quantitative metallography revealed beta grain refinement achieved primarily through static/metadynamic recrystallization. The beta recrystallization kinetics were subsequently predicted through an Avrami-type relationship.

Abstract: Plasma processing has been developed to produce selective chemistry in the inner surface of a microfluidic system. This dry process is an alternative solution to the Chemical Vapor Deposition (CVD) process that allows us to work at low temperatures thus avoiding the degradation of the substrate by heat. The present study focused on the surface modification of PDMS in order to make them more hydrophilic and capable to exhibit a high percentage of COOH functions which will provide a good asset for future cell attachment.

Abstract: The paper focuses on the characteristic local network structure of icosahedra observed in the relaxed amorphous metals and its contribution to their elastic properties. Using molecular dynamics method, CuxZr100-x binary amorphous models are constructed by rapidly quenching process from liquid. Voronoi polyhedron analyses expose the existence of the medium-range local network structure composed of inter-penetrating icosahedra. It is found that the globally averaged shear modulus obtained from the atomistically defined elastic moduli decreases with increasing free volume content in the condensed matter. The contribution of the densely packed icosahedral cluster with higher elastic rigidity to the global elastic modulus is discussed.

Abstract: The Cu-line patterns with different linewidth were deposited by radio-frequency sputtering and defined by photolithography lift-off process. The residual stress was evaluated with X-ray diffraction technique and the results show that the Cu-line patterns are in a biaxial stress state and the stress values have a great dependence on linewidth. Further analysis reveals that the intrinsic stress has a main effect on changes of residual stress; however, the thermal stress plays a key role on anisotropic contribution of residual stress in directions along and across the Cu line. The variation of intrinsic stress correlates well with crystal orientation of the Cu line, and the linewidth seems to be the most crucial parameter for evolution of both texture and stress.

Abstract: The material constitutive behaviour and microstructure of Aluminium alloys 6082 and 7449 were studied with the Gleeble hot compression test. The novel aspect of the work is that the testing was done at high strain-rates and at temperatures within 5 K of the solidus. The results indicated that the strength was maintained up to near solidus temperatures, with no dramatic strength reduction being observed. There was however, a distinct change in the slope observed with the 7449 results around 720 K. The experimental results were then fit to the Zener-Holloman equation, which describes the relationship between the material flow stress, temperature and strain-rates. The material microstructure of the hot compression test samples was analysed, and the averaged grain size was calculated to compare with friction stir weld nuggets. This will be used to infer the processing conditions that exist in the dynamically recrystallized weld nugget. Finally, a simple model was used to understand how processing conditions affected the deformation behaviour.

Abstract: Characteristic features of elastic deformation of dies and presses during deep drawing were measured to examine the effects of elastic deformation of the press and dies on product accuracy. Strains were measured on the press including dies, a slide and a bolster of a servo press. A strain magnitude of 63 ×10-6 was obtained when the slide position was at the lowest point. Two slide motions of the servo press were selected to determine appropriate manufacturing conditions. An elastic deformation analysis of the die structure was then performed by CAD simulation. To find an appropriate die structure model, the vertical displacement of the die structure in the CAD simulation was compared to the experiment results. It was found that the vertical displacement of the die structure was 0.147 [mm] at the top surface of the die when considering elastic deformation of the die structure as well as the bolster of the servo press.