Materials Science Forum Vol. 752

Abstract: The examination of solid state processes leading to the degradation of the shape memory behaviour is essential with respect to the suitability of shape memory alloys. Besides degradation processes occurring during relatively long periods of time called ageing, bainitic reactions that suddenly degrade the shape memory behaviour were also observed in many Cu-based shape memory alloys. The mechanisms and effects of the bainitic reactions on the shape memory characteristics were investigated in many Cu-based systems, but the kinetic of the reaction was not examined so far. In the present paper, an examination was carried out on a CuAlNiMn and a CuAlNiMnFe shape memory alloy to reveal what kinetic model describes the bainitic reaction occurring and thus completely destroying the shape memory effect during one stage of heating.

Abstract: Bulk, surface and interface thermodynamics of immiscible liquid alloys are considered within a unified theoretical framework. For bulk thermodynamic functions the exponential and the combined linear-exponential equations are discussed, obeying the 4th law of thermodynamics. Surface phase transition is discussed in details. For surface and interface thermodynamics the monolayer Butler equation is compared to the multilayer model. During further assessment of bulk thermodynamic data of immiscible liquid alloys their experimentally measured surface tension and interfacial energy should be also taken into account, coupled with the models presented here.

Abstract: In the research work the precipitation hardening and/or equal channel angular pressing (ECAP) of PM aluminium alloy (AlCuSiMg) samples were investigated. The aim of the research was to determine the optimal parameters for precipitation hardening, especially temperature and time (in terms of maximal strength), and to test the ECAP pressing number for the same properties of precipitation hardened samples. The samples produced were studied by SEM, X-ray diffraction. The results showed that the PM samples had higher mechanical properties after one pressing by ECAP than after precipitation hardening with optimal parameters. In severe plastic deformation a heated die with a channel angle of 90° and ‘A’ route was used. During the heat treatment the applied temperature of the solution treatment was 420-540°C for 1 hour or 3 hours, and hardening was applied at 180°C for 5 hours.

Abstract: This research work dealt with production of amorphous powder with nominal composition of (Cu₅₅Zr₄₅Al₁₀)₉₇Hf₃ (at%). Combining the mechanical milling and alloying, powder of crystalline Cu-Zr-Al alloy mixed with Hf elemental powder were milled in order to produce a homogenous and amorphous alloy powder The master alloy and the powders milled for different time were analyzed by X-Ray Analysis (XRD) and Scanning Electron Microscopy (SEM). Particle size distribution and hardness were controlled during milling and at the end of procedure. The milling caused dissolving of the hafnium. The 25 h milling time was the optimal to obtain the Hf containing powder with amorphous structure. However, elemental Hf traces with size below 3 µm were still observed in the powder. After 50 h of milling, such impurity elements as iron, nickel, chromium originating from milling tools (vial, balls) were detected.

Abstract: This paper reports the results of ED-XRF method for the determination of low-level contaminated solders. The method was calibrated for the analysis of part-per-million (ppm) levels of Pb and major levels of other elements. In this work, two types of Sn-Ag based solder alloys are used; the ternary Sn-3.0wt%Ag-0.5wt%Cu (SAC305) and the 6-part Sn-3.5wt%Ag-3.2wt%Bi-1.6wt%Sb-0.5wt%Cu-0.15wt%Ni were examined. Empirical calibration and fundamental parameter calibration were used to analyze samples. The results of this study demonstrate the differences between the applied calibration methods for detection of Pb. Screening analysis of bulk samples from variant production lines were also discussed.

Abstract: The European Union and Japan initiated the issue of RoHS, the directive about the restriction of hazardous substances, which prohibits certain hazardous substances in electronic equipment - including lead - application. Due to the directive the use of lead free solder alloys is spreaded, however the Pb in the form of contamination may be appear under technological process. The lead impurity has significant effect on microstrucutre and lifetime so it is necessary to carry out detailed examinations. In this paper the study of intermetallic compounds in six-element, Pb impured, thermal cycles test-subjected, Sn-Ag-Cu (SAC) solder alloy is demonstrated

Abstract: Composites are special material which can provide individual properties such as high strength with low density or good thermal conductivity with low thermal expansion coefficient. Composites conform to the constantly evolving and more complex expectations. In order to make a product with good quality, it is important to choose suitable materials and technology. In this research powder metallurgy (PM), as one of the most common composite manufacturing technology, was examined -which factors and mechanisms influence mostly the properties of the product. Ishikawa method was used to reveal these correlations.

Abstract: Al–7wt.-% Si–1wt.-% Fe alloy was solidified unidirectionally in the Crystallizer with High Rotating Magnetic Field (CHRMF). The diameter of sample was 8 mm and its length was 120 mm. The parameters of solidification were as follows: solid/liquid interface velocity ~0.082 mm/s, temperature gradient 7+/-1 K/mm, magnetic induction 0 and 150 mT, frequency of magnetic field 0 and 50 Hz. The structure solidified without rotating magnetic field (RMF) showed a homogeneous, columnar dendritic one. The structure solidified by using magnetic stirring showed a dual periodicity. On the one hand, the branches of the “Christmas tree”-like structure known from the earlier experiments contained Al+Si binary eutectic. On the other hand, bands with higher Fe- and Si-content formed in the sample, which were at a larger distance from each other than the branches of the “Christmas tree” structure. The developed microstructure was analyzed by SEM with EDS. The average Si- and Fe-concentrations were measured on the longitudinal section at given places along the length of sample. Furthermore the Si- and the Fe-concentrations close to the bands and among the bands as well as the composition of the compound phases were determined.

Abstract: The constitutive equation in hot working for Al 7075 aluminum alloy was obtained employing experimental data of stress-strain curve, in a wide range of temperature (250-450°C) and strain rate (0.002-2 s-1). The influence of temperature and strain rate on the deformation behavior is represented by the equation proposed by Sellar and McTegart, all material parameters are considered as function of equivalent strain. The force-height data was corrected with interpolation method in the way to eliminate the error at the measurement. To verify the constitutive equation two parameter were calculated average absolute relative error (AARE=6.42) and correlation coefficient (R=0.998), for the same purpose the measuring and calculated flow curve are plotted together, the results shows that the constitutive equation obtained is good describing the behavior of the material.