Influence of the Test Configuration and Temperature on the Mechanical Behaviour of WC-Co

Luis M González,Raul Bermejo,Ernesto Chicardi,Yadir Torres,Francisco J Gotor,Luis Llanes

doi:10.3390/met10030322

Luis M González, Raul Bermejo + Show 4 more

Open Access

https://doi.org/10.3390/met10030322

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Abstract

In this work, the effect of the test configuration and temperature on the mechanical behaviour of cemented carbides (WC-Co) with different carbide grain sizes (dWC) and cobalt volume fractions (VCo), implying different binder mean free paths (λCo), was studied. The mechanical strength was measured at 600 °C with bar-shaped specimens subjected to uniaxial four-point bending (4PB) tests and with disc specimens subjected to biaxial ball-on-three-balls (B3B) tests. The results were analysed within the frame of the Weibull theory and compared with strength measurements performed at room temperature under the same loading conditions. A mechanical degradation greater than 30% was observed when the samples were tested at 600 °C due to oxidation phenomena, but higher Weibull moduli were obtained as a result of narrower defect size distributions. A fractographic analysis was conducted with broken specimens from each test configuration. The number of fragments (Nf) and the macroscopic fracture surface were related to the flexural strength and fracture toughness of WC-Co. For a given number of fragments, higher mechanical strength values were always obtained for WC-Co grades with higher KIc. The observed differences were discussed based on a linear elastic fracture mechanics (LEFM) model, taking into account the effect of the temperature and microstructure of the cemented carbides on the mechanical strength.

Highlights

Rising competitiveness in the metal industry is driving a continuous reduction in manufacturing time and associated costs
It can be speculated that the intrinsic defects associated with processing may have experienced subcritical crack growth, associated with R-curve behaviour. This behaviour can be the result of a lower oxidation extent for this material grade, which is in agreement with the results reported by Basu and Sarin [18], in which higher oxidation was observed in WC-Co as the Co content was reduced
This fact is more clearly observed at 600 ◦ C, where the defect size distribution becomes more homogeneous, in such a way that the differences were reduced between the largest flaw populations that induced failure in the highly stressed region corresponding to each test configuration

Summary

Introduction

Rising competitiveness in the metal industry is driving a continuous reduction in manufacturing time and associated costs. Measurement uncertainties associated with the experimental procedure (inaccurate positioning of the specimens, uneven contact, and transfer of load, friction, etc.) can lead to the underestimation of the Weibull parameters, which is more critical in the case of materials with relatively high Weibull moduli because these uncertainties may be in the range of the scatter of the strength values [11]. Biaxial bending tests, such as the ball-on-three balls (B3B) test [12,13], are attracting increasing interest to overcome the problem of introducing defects during sample preparation. Three sintered cemented carbide grades (referred to as 16F, 16M, and 27C) with different

Materials and Experimental

Results and Discussion

Conclusions