Compressive stresses in cemented carbide

Sammanfattning: This master thesis work aims towards gaining a deeper understanding of residualstresses in cemented carbide rock drill inserts. Compressive stresses are wanted inthe surface material since they prevent crack growth and wear of the material andthis work is part of the development of better and longer lasting inserts.Different ways of measuring residual stress with 2-dimensional x-ray diffraction areinvestigated. Also different surface treatment methods, used for attaining thesecompressive stresses, are tested and evaluated by measuring surface residual stress.Also hardness and residual stress in-depth profiles are measured by cutting treatedinserts in half and perform measurement on cross sections.The results show that measurements can be conducted on the raw sample surfacewith a 0.5 mm x-ray spot size. The effectiveness of surface treatments varies withdifferent cemented carbide grades. Blasting gives rise to the highest compressivestresses in a harder cemented carbide grade while it produces a lot of crushedtungsten carbide grains and similar stresses as tumbling in a softer grade. Treatment Tgives interesting result since it produces high compressive stress but still leaves thesurface grains unbroken. Attempts to measure both hardness and residual stressgradients from the surface are found to be difficult. Large effects from samplepreparation and deviations in measured data give uncertain results but tumbling seemsto affect the material deeper down from the surface compared to both blasting andtreatment T. This is also confirmed by a larger increase of coercive field strength intumbled samples.