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[Display omitted] • The ball mill edge-chipping test is a new laboratory device designed for superior replication of in-field loading modes. • Consistent with life-limiting damage modes in service, its fracture mechanism includes crack initiation, instead of artificially excluding this step. • It offers rapid, low-cost production of fracture resistance data for purposes of materials selection. • Rather than being deterministic, it adopts a stochastic approach, measuring volume loss accumulated from hundreds of small fracture events. Abrasion-resistant materials for rock-facing applications typically display low fracture toughness. For materials selection, available fracture data are limited, due to the cost of testing. To address this shortage, a new type of fracture test, denoted the ball mill edge chipping test (BMECT), has been designed. The device is derived from the ball mill abrasion test (BMAT) [37]. It uses simple block or ball specimens with machined edges. Specimens of multiple materials are tested simultaneously. Collisions promote multiple small-scale fracture events at the exposed edges, causing progressive volume loss. The reciprocal of volume loss indicates relative fracture resistance. This paper analyses the BMECT's relevance to service, and explores its capacity to generate data at low cost. Several data sets are presented, illustrating its application to investigate factors affecting fracture resistance among common abrasion-resistant materials. The results demonstrate multiple advantages over traditional fracture tests — including low cost, high sensitivity to differentiate between materials, and close replication of in-service damage modes. It represents a fundamentally new approach to fracture resistance assessment. Whereas traditional tests are regarded as deterministic, the BMECT is stochastic , providing potential for superior statistical data quality. [ABSTRACT FROM AUTHOR]

The addition of NbC to high chromium white cast irons (WCIs) has potential to improve component wear lives in mining and ore beneficiation environments, due to the combined presence of Cr-rich and niobium carbides. While the effect of chromium carbide volume fraction (Cr-CVF) on abrasion performance of plain-Cr WCIs is well understood, its effect on NbC-bearing WCIs is unknown. This work studies the effect of Cr-CVF on high-stress abrasion of this newer class of dual-reinforced high-Cr WCIs, using the ball mill abrasion test with quartzite and basalt. The alloys cover a wide range of Cr-CVF, from M 7 C 3 -free NbC-reinforced steel to hyper-eutectic WCI. Bulk hardness increased linearly with Cr-CVF, at a rate of 3.9 HV per 1% Cr-CVF. In basalt, abrasion resistance increased linearly with Cr-CVF, at an average life improvement rate of 24% per 1% Cr-CVF. This confirms that performance is maximized by increasing Cr-CVF even in the presence of substantial volumes of cubic carbides. In quartzite the trend is again linear up to 30 vol% M 7 C 3 (3.7% life increase per 1% Cr-CVF), but the hyper-eutectic alloy shows poorer resistance than slightly hypo-eutectic alloy. SEM studies of the worn surfaces demonstrate that micro-fracture of the hard carbides was the controlling damage mechanism. Primary M 7 C 3 was observed to suffer fragmentation in high-stress abrasion in quartzite, confirming the expectation from the quantitative trend. • Cr-rich carbides show great promise in improving hardness and abrasion resistance of NbC-bearing high-Cr white cast irons. • Increasing Cr-rich carbides fraction increased hardness linearly in the range of carbide-free steel to hyper-eutectic iron. • High-stress abrasion performance showed positive correlation with the volume fraction of Cr-rich carbides. • In competent abrasive rock, the beneficial effect of Cr-rich carbides on abrasion life was limited to hypo-eutectic irons. • Micro-fracture of hard carbides was the controlling wear mechanism, strongly manifested in primary Cr-rich carbides. [ABSTRACT FROM AUTHOR]

Wear behavior of white cast irons (WCIs) is largely attributable to the particulate-reinforced composite phenomenon, in which both reinforcing particles and matrix play important roles. In high-Cr WCIs, matrix properties are influenced by chromium-to-carbon (Cr:C) ratio. Without a strong matrix, the carbides would not have sufficient support during the abrasion interactions. The effects of Cr:C ratio on the wear properties of plain-Cr WCIs have been only partially studied; but its effect on Nb-containing WCIs has never been explored. This work studies the influence of Cr:C ratio on high-stress abrasion performance of WCIs further reinforced by niobium carbides (NbC). The alloys covered wide range of Cr:C ratios, resulting in considerable variation in hardness — low hardness for both very-low and very-high Cr:C. Abrasion resistance was assessed by the ball mill abrasion test in quartzite and basalt, showing an optimum matrix Cr:C around 14.6 and 18, respectively. The very-high Cr:C alloy exhibited poorest resistance in both abrasives, and the very-low Cr:C alloy was second-poorest. SEM of worn surfaces revealed the effects of Cr:C ratio on the type and level of damages to microstructure, manifested by various morphologies and depths of indentations and grooves on the matrix, and various types and severities of damages to Cr-rich carbides, including micro-cutting and micro-fracture. NbC particles appeared to be protective across the full range of Cr:C ratios. [Display omitted] • Matrix properties, influenced by Cr-to-C ratio, has strong effect on abrasion resistance of white cast irons. • In NbC-bearing high-Cr white irons, variations of matrix Cr:C ratios resulted in significant variations in bulk hardness. • High-stress abrasion performance, assessed by ball mill abrasion test, showed an optimum at matrix Cr:C ratio of 14.6–18. • In both less-competent and competent abrasives, very-high and very-low Cr:C showed poor high-stress abrasion performance. • SEM studies of worn surfaces revealed the strong effect of Cr:C on the type and level of damages to microstructure. [ABSTRACT FROM AUTHOR]

[Display omitted] • High chromium white cast irons containing niobium macro-additions show great promise in abrasive wear applications. • Increasing niobium content of the alloy linearly increased the hardness of heat-treated dual-reinforced hypo-eutectic high-Cr white irons. • Clear beneficial effect of Nb macro-addition on abrasive wear behaviour was observed under both less-competent and competent abrasive rocks. • In optimum addition ranges, life improvements of 37% and 7% per 1 wt%Nb were achieved under less-competent and competent abrasives, respectively. • Resultant NbC particles mostly protruded above matrix and Cr-rich carbides in the wear scars under controlling wear mechanism of micro-fracture. Abrasive wear is a principal cost in mining and mineral processing operations. High chromium white cast iron (WCI) further reinforced with niobium carbide (NbC) shows promise to increase component wear lives. This work investigates the effect of niobium macro-additions on microstructure, hardness and high-stress abrasive wear behaviour of Nb-containing high-Cr WCIs. Eight alloys with Nb between 0 and 10.7 wt% were produced by sand casting. Increasing niobium carbide volume fraction (Nb-CVF) increased hardness from 724 to 812 HV (7.3 HV per 1% Nb-CVF). Abrasive wear resistance, assessed using the ball mill abrasion test in basalt (less competent) and quartzite (competent rock), showed clear beneficial effect of NbC macro-addition up to 11.4 and 7 vol% in basalt and quartzite, respectively. These correspond to life improvements of 37% and 7% per 1% Nb-CVF in the optimum range of Nb macro-addition, in basalt and quartzite respectively. Micro-mechanistic observations of worn surfaces showed that NbC particles not only protrude from the matrix but do so more than Cr-rich M 7 C 3 carbides. In deep wear grooves created by quartzite, M 7 C 3 particles were cut flush with the matrix, whereas NbC protruded, visibly impeding the progress of the abrasion event. [ABSTRACT FROM AUTHOR]

• Analysis methodology is influenced by geographical culture [1] and industry culture of the analyst. • There is a requirement to acknowledge and understand the criticality of cultural and industry bias. • This will allow an objective rigour to the selection of the forensic analysis methodology to be applied. • This will mitigate subjective reasoning and reduce the risk and cost of the decision-making process. Booker et al. [3] stated that " in many engineering defect investigations, the choice of forensic analysis methodology is rarely questioned, and the forensic analysis methodology is chosen by the analyst without due diligence, resulting in a methodology that may not be the most accurate or expedient. This in turn has the potential to increase the risk and cost of the decision-making process." Therefore, a need was identified to identify and analyse the variables that influence practitioners' selection of an appropriate forensic analysis methodology. A review of current literature highlighted the fact that there was no definitive correlation identifying the primary variables that affect the selection of forensic analysis methodology. Noting that the determination of the correct methodology for a specific instance is not within scope of this paper, the first stage of the analysis was to apply previously collated methodology taxonomy, and then apply Principal Component Analysis (PCA) to determine which variables had the highest significance of influence on the selection of Forensic Analysis Methodology from 132 case studies selected from Case Studies in Engineering Failure Analysis [2] (Appendix A.). The analysis has determined that the methodology selected to conduct forensic analysis is primarily influenced by the geographical culture and industry of the analyst. Therefore, there is a requirement to acknowledge and understand the role of cultural and industry biases when choosing an appropriate methodology, and subsequently, when evaluating a forensic analysis case study. Although the mere recognition of the existence of cultural and industry bias does not guarantee that the right decisions will be made, it does, however, facilitate an objective rigour to the process of the selection of the forensic analysis methodology to be applied, which in turn, will mitigate subjective reasoning and potentially reduce the risk and cost of the decision-making process. Without an international standard for forensic analysis, or universally acknowledged guidelines for the selection of forensic analysis methodology, analysts will continue to be susceptible to methodology selection bias, which will increase the probability of choosing a sub-optimal methodology, which, in turn, can prolong the investigation and adversely affect the accuracy of the analysis. [ABSTRACT FROM AUTHOR]

NiHard-4 and high-Cr-Mo white cast irons are two classes of abrasion-resistant cast irons extensively utilized in mining and related industries. Despite widespread usage, systematic performance comparisons between the two classes are lacking. Using four exemplar NiHard-4 and four exemplar high-Cr-Mo WCIs, this study compares the abrasive wear performance of the two alloy classes under a variety of conditions. The wear tests were the dry sand rubber wheel abrasion test (DS-RWAT), inner circumference abrasion test (ICAT) with quartzite, and ICAT with basalt. The resulting quantitative trends were interpreted and explained using bulk hardness, microhardness and nanohardness measurements, coupled with SEM of microstructures and worn surfaces. In all three abrasion tests the average wear life of high-Cr-Mo WCI was superior to NiHard-4. Average life improvements were 20% in DS-RWAT, 77% in ICAT-quartzite and 124% in ICAT-basalt. In the DS-RWAT there was overlap in the data and the difference between the two alloy classes was not statistically significant, but in the ICAT, for both rock types the two classes were strongly differentiated. Of various hypotheses considered to explain the results, the experimental evidence required that differences in carbide volume fraction or matrix hardness must be rejected. Instead it was shown that the superior performance of high-Cr-Mo WCIs was due primarily to their higher Cr:C ratio, resulting in higher Cr:Fe ratio and therefore elevated hardness and fracture toughness of the eutectic carbides. • Outcomes revealed superior abrasion performance of high-Cr-Mo over NiHard-4 abrasion-resistant white cast irons. • Cr:C ratio was identified as the dominant microstructural feature for the superiority of high-Cr-Mo over NiHard-4 alloys. • Higher Cr:C ratio in high-Cr-Mo, leads to higher Cr:Fe ratio in (Cr,Fe) 7 C 3 eutectic carbides than those in NiHard-4. • Higher Cr:Fe ratio in (Cr,Fe) 7 C 3 eutectic carbides, provides elevated hardness and fracture-toughness for these compounds. [ABSTRACT FROM AUTHOR]

• The selection and rigour of failure analysis methodology has a direct impact on the accuracy and expediency of the decision-making process. • It has been established that no internationally recognised standard or diagnostic accuracy guidelines exist for engineering failure analysis. • At present, the outcome of failure analysis is an opinion, albeit a considered one. • Currently a failure analysis methodology is chosen by the analyst without due diligence and applied according to their interpretation. • It has been established that there is a need for an internationally recognised failure analysis standard and diagnostic accuracy guidelines as a calcification of ideas, codified and clarified. At present, the outcome of failure analysis is an opinion, albeit a considered one, based on the best facts available informed by a series of non-standardised diagnostic tests and experience. Acknowledging that there are many tools that have been developed and implemented successfully by failure analysts over many years, this paper specifically identifies the need for: a. an internationally recognised failure analysis standard; and. b. diagnostic accuracy guidelines. It is hypothesised that a standard is required to make the process repeatable so that the results can be peer reviewed, lessons learned, and the outcome be objective. Through a thorough literature review and the analysis of 132 failure analysis case studies, various failure analysis methodologies were identified, and diagnostic accuracy methodologies appraised. It was concluded that currently a failure analysis methodology is typically chosen by the analysts without a critical selection process. The methodology chosen is then applied according to their interpretation, which in turn yields a diagnostic decision. Consequently, the chosen methodology may not be the most accurate or expedient, which has the potential to increase the risk and cost of the decision-making process. It is recommended that a structured approach to decision analysis be established, leading to a set of diagnostic accuracy guidelines, which, once adopted and implemented by the engineering fraternity, allows the further development of an internationally recognised failure analysis standard, thereby reducing the risk of misdiagnosis and repetition of the failure. [ABSTRACT FROM AUTHOR]