Influence of WC-Co hard metal microstructure on defect density, initiation and propagation kinetics of fatigue cracks starting at intrinsic and artificial defects under a negative stress ratio

Klünsner, Thomas; Gettinger, C. L.; Walch, L.; Pippan, Reinhard

doi:10.1016/j.actamat.2020.01.057

Cited by 28 publications

(10 citation statements)

References 37 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Scanning Electron Microscope (SEM), TM3030 Hitachi backscatter SE, was used to view the surface topography in particular to identify microstructure boundaries, cracks, thermal shock, voids, pores, splatter and balling as a result of laser processing. These defects affects the performance of a material in application [24].…”

Section: Characterisationmentioning

confidence: 99%

“…This caused cracks and geometric distortions. A higher weight percentage of WC would reduce this effect if the same parameters were used as less of the binder would be present to induce stresses [24]. Khmyrov et al [31] showed this when laser sintering WC-Co of equal weight percentages, and found many cracks due to the formation of W 3 Co 3 C brittle phases.…”

Section: Wc Comentioning

confidence: 99%

See 1 more Smart Citation

Understanding The Surface Integrity of Laser Surface Engineered Tungsten Carbide

Hazzan

Pacella

See

2021

Preprint

View full text Add to dashboard Cite

The study investigated the effect of fibre laser processing (1060 nm, 240 ns pulse duration) on tungsten carbide (WC). Fluence, frequency, and the interaction effect of these were the most influential factors on the surface integrity and crack formation. In this paper, a crack classification system was developed, and a crack density variable was introduced to estimate the number of cracks and crack type within a 1 mm2 area size. ANOVA was used to analyse how fluence (0.05–0.20 J/cm2) and frequency (5–100 kHz) altered the crack density. The crack density increased between 0.050–0.099 J/cm2 across all frequency settings then decreased as the fluence increased to 0.20 J/cm2. Superficial cracks were present in all frequency settings but particularly with lower fluence settings. Micro-cracks were more likely to form between 0.050–0.135 J/cm2. Deep cracks did not present until 40 kHz or above 0.099 J/cm2 across the frequency settings and were situated around balling and splatter defects. The crack density was minimised at 0.149 J/cm2 fluence and 52.5 kHz. To the author’s knowledge for the first time a quantitative analysis of the crack formation mechanism for brittle materials is proposed (post laser processing). In addition, a linear model generated to predict surface roughness performed best at moderate to medium level of processing (fluences in the region of 0.050–0.099 J/cm2) with an error between 1 % to 10 %. The model failed to predict the material response as accurately at higher fluences with percentage errors between 15 % to 36 %.

show abstract

Section: Characterisationmentioning

confidence: 99%

Section: Wc Comentioning

confidence: 99%

Understanding The Surface Integrity of Laser Surface Engineered Tungsten Carbide

Hazzan

Pacella

See

2021

Preprint

View full text Add to dashboard Cite

show abstract

“…Scanning electron microscope (SEM), TM3030 Hitachi backscatter SEM, was used to view the surface topography in particular to identify microstructure defects such as cracks, thermal shock, voids, pores, splatter and balling as a result of laser processing. These defects affect the performance of a material in application [30]. Energy-dispersive spectroscopy (EDS) analysis for chemical composition was also applied in various regions.…”

Section: Characterisationmentioning

confidence: 99%

“…This caused cracks and geometric distortions. A higher weight percentage of WC would reduce this effect if the same parameters were used as less of the binder would be present to induce stresses [30]. Khmyrov et al [39] showed this when laser sintering WC-Co of equal weight percentages and found many cracks due to the formation of W 3 Co 3 C brittle phases.…”

Section: Wc Comentioning

confidence: 99%

Understanding the surface integrity of laser surface engineered tungsten carbide

Hazzan

Pacella

See

2021

Int J Adv Manuf Technol

View full text Add to dashboard Cite

The study investigated the effect of fibre laser processing (1060 nm, 240-ns pulse duration) on the surface integrity of tungsten carbide (WC). The induced surface damage ranged from crack formation, porosity, balling, to spherical pores; the severity and presence of each were dependent on the laser parameters selected. The influence of fluence (0.05–0.20 J/cm2), frequency (5–100 kHz), feed speed (250–2500 mm/s) and hatch distance (0.02–0.06 mm) on 2D and 3D surface roughness were analysed using the Taguchi technique. Fluence, frequency, and the interaction effect of these were the most influential factors on the surface integrity; from this a linear model was generated to predict the surface roughness. The model performed best at moderate to medium level of processing with an error between 1 and 10 %. The model failed to predict the material response as accurately at higher fluences with percentage errors between 15 and 36 %. In this study, a crack classification system and crack density variable were introduced to estimate the number of cracks and crack type within a 1-mm2 area size. Statistical analysis of variance (ANOVA) found that fluence (63.49%) and frequency (29.38%) had a significant effect on the crack density independently but not the interaction of both. The crack density was minimised at 0.149 J/cm2 and 52.5 kHz. To the author’s knowledge, for the first time, a quantitative analysis of the crack formation mechanism for brittle materials is proposed (post laser processing).

show abstract

“…The influence of phase transformation on wear behavior is another research topic [39]. Fatigue damage evolution is an important investigation aspect for tool materials, e.g., [43,44]. Some studies concentrate on microscopic issues, such as grain boundary energies, crystal orientations, and grain coatings [45][46][47].…”

Section: Introductionmentioning

confidence: 99%

Experimental Investigations of Micro-Meso Damage Evolution for a Co/WC-Type Tool Material with Application of Digital Image Correlation and Machine Learning

Schneider

Zielke

et al. 2021

Materials

View full text Add to dashboard Cite

Commercial Co/WC/diamond composites are hard metals and very useful as a kind of tool material, for which both ductile and quasi-brittle behaviors are possible. This work experimentally investigates their damage evolution dependence on microstructural features. The current study investigates a different type of Co/WC-type tool material which contains 90vol.% Co instead of the usual < 50vol.%. The studied composites showed quasi-brittle behavior. An in-house-designed testing machine realizes the in-situ micro-computed tomography (CT) under loading. This advanced equipment can record local damage in 3D during the loading. The digital image correlation technique delivers local displacement/strain maps in 2D and 3D based on tomographic images. As shown by nanoindentation tests, matrix regions near diamond particles do not possess higher hardness values than other regions. Since local positions with high stress are often coincident with those with high strain, diamonds, which aim to achieve composites with high hardnesses, contribute to the strength less than the WC phase. Samples that illustrated quasi-brittle behavior possess about 100–130 MPa higher tensile strengths than those with ductile behavior. Voids and their connections (forming mini/small cracks) dominant the detected damages, which means void initiation, growth, and coalescence should be the damage mechanisms. The void appears in the form of debonding. Still, it is uncovered that debonding between Co-diamonds plays a major role in provoking fatal fractures for composites with quasi-brittle behavior. An optimized microstructure should avoid diamond clusters and their local volume concentrations. To improve the time efficiency and the object-identification accuracy in CT image segmentation, machine learning (ML), U-Net in the convolutional neural network (deep learning), is applied. This method takes only about 40 min to segment more than 700 images, i.e., a great improvement of the time efficiency compared to the manual work and the accuracy maintained. The results mentioned above demonstrate knowledge about the strengthening and damage mechanisms for Co/WC/diamond composites with > 50vol.% Co. The material properties for such tool materials (> 50vol.% Co) is rarely published until now. Efforts made in the ML part contribute to the realization of autonomous processing procedures in big-data-driven science applied in materials science.

show abstract

Influence of WC-Co hard metal microstructure on defect density, initiation and propagation kinetics of fatigue cracks starting at intrinsic and artificial defects under a negative stress ratio

Cited by 28 publications

References 37 publications

Understanding The Surface Integrity of Laser Surface Engineered Tungsten Carbide

Understanding The Surface Integrity of Laser Surface Engineered Tungsten Carbide

Understanding the surface integrity of laser surface engineered tungsten carbide

Experimental Investigations of Micro-Meso Damage Evolution for a Co/WC-Type Tool Material with Application of Digital Image Correlation and Machine Learning

Contact Info

Product

Resources

About