The industrial challenge

Hard metal, composed of tungsten carbide (WC) particles bound together by Cobalt (Co)-rich binder, is the material choice for tools for metal cutting and rock drilling. During operation, the tools can reach temperatures exceeding 900°C, and since they are subjected to significant mechanical stress, the residual stresses become an important parameter affecting the performance. These stresses activate several mechanisms which can lead to deformation and finally to failure of the tool. Up to three times longer cutting tool life can be achieved by Chromium (Cr) additions in cemented carbides. The mechanistic understanding of the improved properties by Cr-doping is thus critical for accelerating innovations and reducing the lead-time for product development. 

Sandvik is a multinational engineering company based in Sweden. They took their engineering challenge to Scatterin, a neutron and synchrotron X-ray service and software provider that was spun out from research at KTH Royal Institute of Technology in Stockholm. In collaboration with researchers from KTH and Chalmers University of Technology , they came to ISIS through the Industrial Collaborative R&D (ICRD) programme to gain understanding of the high-temperature deformation mechanisms in Cr-doped hard metals by using in-situ neutron scattering.​

​The benefits of using ISIS

Available lab-scale analyses are constrained to examining very small sample volumes with limited in-situ capabilities, preventing the complete quantitative view of the structural evolution in mimicked production and service conditions. Furthermore, the poor penetration depth of X-rays in materials made of heavy elements, such as W, makes neutron diffraction (ND) and small-angle neutron scattering (SANS) the most suitable characterisation techniques to investigate cemented carbides as bulk material. Additionally, the magnetic scattering of the cobalt makes SANS suitable also to separate signal stemming from the binder and secondary carbide phase.​

The in-situ SANS experiments were performed on the Larmor instrument at ISIS, using the Delft furnace to monitor the WC/Co interface structure evolution and precipitation of secondary carbides up to 1000 °C. The figure shows the in-situ setup, where the high temperature furnace positioned inside a magnet. The SANS experiments were complemented by room temperature residual stress measurements using ND on the Engin-X instrument. The sample matrix consisted of five hard metal compositions representing various WC grain size and Cr/Ti additions. Whilst cylindrical samples with 6 mm diameter were used for ND, plate specimens with 12 mm diameter and 0.3 mm thickness were used in SANS experiments. The analysis of reduced ND and SANS data were performed on Scatterin SaaS software. To complement and validate the neutron scattering results, also lab-scale atom probe tomography (APT) and electron backscatter diffraction (EBSD) investigations were performed. 

The results and expected impact

The in-situ SANS experiments provided previously unattainable information on the evolution of microstructure associated with formation, dissolution, and growth of e.g. interfacial layers and larger carbides in hard metals. The ND measurements could reveal the influence of dopants on the residual stresses in hard metals. Whilst the addition of Cr was found to increase residual stress in the WC particles, the addition of Ti resulted in reduced residual stress in WC. This project has not only provided important information on microstructural evolution of Cr-doped hard metals but has also expanded our experience on available sample environments for demanding in-situ SANS experiments.  

“Bulk measurements of material properties in-situ using neutron scattering at simulated operating conditions, will help us to further understand and develop our materials and tools,” says Fredrik Lindberg from Sandvik Coromant.

This research was funded by Sweden’s Innovation Agency, Vinnova, in order to build competence and capacity regarding industrial utilisation of large-scale research infrastructures such as MAX IV and ESS. 

This article originally appeared on the Vinnova website. 

The work has recently been published in the International Journal of Refractory Metals and Hard Materials, Volume 128, April 2025, 107005, DOI: 10.1016/j.ijrmhm.2024.107005​