Volume 79, Issue 4

Surface heat treatments such as case hardening, nitriding and surface hardening are often used to improve the performance properties of gear components. Due to limitations in the individual processes, e. g., with regard to the distortion that occurs, the achievable hardening depth or surface hardness, combinations of several processes are important in order to achieve better process efficiency and component properties. The present investigations focus on dimensional and shape changes in the combination of nitriding and induction hardening on samples and gears made of the materials EN31CrMoV9 and EN42CrMo4, measured before and after the heat treatments. For the gears examined, comparable dimensional and shape changes were determined after the combination treatment as for induction hardening alone, which overall resulted in larger geometric changes than nitriding. Due to the dimensional and shape deviations of the geometric features, reworking by means of gear grinding is advisable in certain cases.

Hot-work tools for hot forming processes, such as die forging, are subject to complex loads that can often lead to premature tool failure. The present study attempts to reduce the main cause of failure of high-speed hot working tools, i. e., wear due to surface breakdown, with the aid of damage-tolerant microstructures. For this purpose, a hot-work tool steel is specifically alloyed with copper in order to form copper precipitations during the subsequent heat treatment, which increase the strength of the material and contribute to the reduction of dislocation movements. The aim is to close the property gap between the standardized direct-hardening and secondary-hardening hot-work tool steels.

The purpose of this study was to explore the effect of eutectic silicon particle size on the properties of composites of carbon-nano tubes (CNTs) and AlSi10Mg prepared by powder metallurgy. The samples were studied using light microscopy, X-ray diffraction, scanning electron microscopy, transmission electron microscopy, friction tests and tensile experiments. The effects of short-term heat treatment (540 °C solid solution for 1 h 175 °C aging for 4, 5, and 6 h) on the microstructure, tribological properties and tensile properties of the CNTs/AlSi10Mg composites were investigated. The results showed that the composite material showed an obvious toughening effect after 1 h of solid solution treatment and 4 h of aging, and the elongation increased by 33 %. Adding CNTs can improve the friction performance of the material. The composite material has the best friction performance when aged for 5 h. After a short heat treatment, the eutectic silicon is homogenized in the α-Al matrix, and the eutectic network is broken. The eutectic silicon becomes rounded from the lath shape. The spheroidized structure reduces stress concentrations around silicon particles and improves the friction performance of the composite material.