In order to improve the hot workability of AISI D2 tool-steel ingots during several heats hot deformation process, laboratory hot-compression tests as well as industrial investigations of the carbides' behaviour were carried out. The conditions that led to the occurrence of undesired, oversized carbides in the matrix were estimated and explained. It was found that to high soaking temperature results in an increased size of carbides which decreases hot workability. The results of industrial investigations show that area fraction of carbides after the end of each deformation cycle remains almost constant, but their mean size more than double during deformations in several heats which implies that the final microstructure is not dependent primarily on the last soaking-deformation cycle but depends on entire processing history, i.e. hot workability over several hot-deformation cycles can change considerably from cycle to cycle.
COBISS.SI-ID: 1287775
Metallurgical characterization of a sword blade dating from the second half of the 15th century found in central Slovenia was performed in order to determine its chemical composition, microstructure, microhardness, and to obtain insight into the methods of manufacture. The results show that the sword was manufactured from a single wrought iron billet. The surface of the sword was carburized. No evidence of quenching was found. The ferritic microstructure is concentrated in the core, and the pearlitic in the outer layer of the blade. This is nice example of bulk functionaly graded material.
COBISS.SI-ID: 1085534
This research aimed to create multifunctional cellulose fibres with waterand oil-repellent, self-cleaning, and flame retardant properties. A sol mixture of fluoroalkyl-functional siloxane, organophosphonate and methylol melamine resin was applied to cotton fabric by the pad-dry-cure method. Successful coating was verified by atomic force microscopy and Fourier transform infrared spectroscopy. The results demonstrate the synergistic activity of the compounds in the coating, which resulted in the creation of a “lotus effect” on the fabric surface as well as excellent flame retardancy and thermal stability.
COBISS.SI-ID: 2936432
Sensitivity analysis of an XFEM crack propagation model is developed for shape and material parameters, where the direct differentiation method is applied to large strain problems with hyperelastic neo-Hookean materials. The presence of level set functions to describe the crack position requires the development of a proper differentiation technique which is also addressed. In order to compute the analytical derivatives of such a complex numerical model the capabilities of the symbolic system AceGen are employed. The techniques presented in this paper can be extended to anisotropic materials and non-linear materials exhibiting plasticity and viscoplasticity. Additionally, this formulation constitutes a base for further analysis of crack branching and crack joining problems.
COBISS.SI-ID: 1418335
The progress of wear associated with the compound and diffusion layers of nitrided samples was studied by employing laboratory tests at low, medium and high contact pressures, simulating the conditions occurring during the hot extrusion of aluminium. It was found that with increasing of contact pressure also wear rates increase that indicates on predominately frictional removal of compound layer . Testing at medium contact pressures reveals some common features observed at testing at lower as well as at higher contact pressures. The essential difference between the testing at medium and low contact pressures is in the density of the obtained micro-craters and appearance of their extension in sliding direction at medium contact pressures. At higher contact pressure, removal of compound layer is already preferentially oriented in sliding direction in the first stage, while at medium contact pressure, this is observed only in later stages of degradation progress.
COBISS.SI-ID: 1452895