The presence of unintentional background impurities found in LPE-grown Hg1-xCdxTe layers has been traced back to the starting materials and different technological steps in the course of preparation of the layers. The purified elements Cd and Te, the binary compounds HgTe and CdTe synthesized from them, VB-grown CdTe monocrystals, LPE source solutions and the final LPE (Hg0.78Cd0.22Te/CdTe) layer/substrate structures have been analysed with regard to their impurity content. Spark source mass spectrometry, atomic absorption spectrophotometry and secondary ion mass spectrometry were the analytical techniques employed. Generally, any high-temperature and handling procedures cause an increase in the concentration of most of the impurities. For CdTe Bridgman ingots, a non-uniform distribution with enrichment in the last-to-freeze part of the as-grown crystal is observed. Furthermore, it was found that the carrier concentration and conductivity type of annealed LPE layers are influenced by the varying impurity levels of substrates from different axial positions within the CdTe ingot. The impurity depth profiles of LPE layers show a gettering effect of the layer surface and the layer/substrate interface resulting in a reduced impurity level in the central part of the layers.

A method is proposed for estimating the value of the shear friction factor using a backward extrusion-type forging. This method uses forging load multiplied by the bottom thickness in a backward extrusion test as a measure to calibrate the friction factor. The advantages of the proposed method are: (1) the friction factor can be determined for forming processes where the interface pressure is high and new surface generation is large, e.g., cold forging and precision forging, and (2) the value of the friction factor can be determined continuously during the forming process. Thus, the performance of a lubricant during the entire test can be monitored.

An empirical method was developed to “correct” isothermal flow stress data and thus account for temperature history effects in non-isothermal forging processes. The method is essentially an iterative procedure that uses an FEM code, such as alpid/deform, and results of non-isothermal forging trials to adjust the isothermal flow stress data. Simulation results, conducted with such data for Ti-6Al-4V investigated here, give predictions that are comparable to the experimental load and metal flow measurements in non-isothermal ring tests. Hence, the approach developed in this study, can be used to: (1) obtain the flow stress behavior under non-isothermal forging conditions; and (2) improve the accuracy of FEM simulations of conventional hot forging processes in general.

In the extrusion of tubes from titanium alloys surface defects are often observed. These defects are related to process variables such as tool geometry and temperature, initial billet temperature, characteristics of the extrusion press and lubrication. Often it is difficult to establish optimum process variables for extruding defect-free tubes through experimentation, because this is costly and time consuming. The application of FEM to study metal flow in extrusion is also difficult because large deformations are present and the FEM mesh distorts very rapidly, requiring numerous remeshings. To overcome this problem and to improve the efficiency of applying FEM to investigate tube extrusion, an automated remeshing procedure was developed. Through this procedure the FEM mesh was automatically updated and the FEM code alpid, version 2.3, was used successfully to simulate metal flow under three different extrusion conditions. The results of these simulations helped to understand the formation of surface defects in the internal surface of extruded tubes. This information is expected to assist in improving tube extrusion operations.

The goal of the current study is to adapt a servo-motor driven multi-action press for forming of sheet metal parts under precise velocity control and variable blankholding force. The Engineering Research Center for Net Shape Manufacturing [ERC/NSM] has developed a computer controlled multi-action press with two independently driven punches for research in cold forming of complex parts, using physical modeling techniques. Recently, the same press was modified and upgraded for use in sheet metal forming. As a result of its special design and construction, this press is highly controllable and can perform a wide range of sheet metal forming processes. Tests were conducted in order to obtain the actual press characteristics. Axisymmetric deep drawing experiments were performed with 1100-O annealed aluminum material using all three actions of the press. In these preliminary experiments, the crucial role of blankholding force control on final product quality and drawability was established.