Towards the perfect neck for HPHT PCD

PCD微观结构的不同对刀具寿命有很大影响。尽管有很多建议，但对哪些因素最重要的具体证据是有限的。因此，对于给定钻探区域的最佳显微组织应该是什么，没有明确的认识，因此也没有明确的加工发展方向。一个重要的例子是颗粒大小的影响。与粗粒级PCD相比，细粒级PCD具有优异的耐磨性，但往往在钻石台面磨损很大程度之前就发生灾难性故障。相反，较粗的牌号磨损更快，但不太容易断裂。这表明损伤容限和耐磨性之间存在着相反的关系。然而，所有显微组织并不是在耐磨性和损伤容限的同一条线上绘制的。我们的目标是了解将PCD推向这样一块地块的右上角的因素，即高耐磨性和长使用寿命，从而能够在不同的条件下定制微观结构来实现这一点。现在有相当丰富的文献涉及(I)在使用过程中发生的一般过程和(Ii)PCD的室温、单调的机械性能。然而，(I)表明，服役期间的局部高温(可能导致石墨化、残余应力或固有性能的改变)和逐渐累积的损伤都是重要的，这与第(Ii)中的实验室工作条件完全不一致。此外，人们认为加工条件的细微差异具有显著的影响(例如，不同制造商表面相似的产品在不同的环境中产生不同的结果)。从上面可以看出，材料科学研究加工/成分/热处理-组织-性能关系是有空间的，但与以往的许多工作相反，重点是对应用重要的条件，如在使用(~800℃)和循环载荷下遇到的温度下的机械性能。此外，最先进的电子、光学和其他表征技术，利用牛津大学广泛的设备和专业知识，将被用来调查由于工艺变化以及随后的热处理和变形而导致的微观结构的差异。研究领域：未来制造主题中的“制造技术”和“材料工程-陶瓷”。

Differences in the microstructure of PCD have an enormous influence on cutter life. Although there are many suggestions, concrete evidence for which factors are most important is limited. As a result, there is no clear understanding of what the optimum microstructure should be for a given drilling region and therefore no clear direction for the future development of processing. An important example is the effect of grain size. Fine grained PCD has excellent wear resistance compared with coarser grained grades but tends to undergo catastrophic failure well before the diamond table has worn away to a great extent. Conversely, coarser grades wear more quickly but are less prone to fracture. This suggests an inverse relationship between damage tolerance and wear resistance. However, all microstructures do not plot on the same line of wear resistance against damage tolerance. The ambition is to understand the factors that move PCD towards the top right hand corner of such a plot, i.e. high wear resistance and long life in service, and hence to be able to tailor the microstructure to achieve this in different conditions. There is now a reasonably rich literature concerning (i) the general processes occurring during service and (ii) the room temperature, monotonic mechanical properties of PCD. However, (i) suggests that both high local temperatures during service (which could cause graphitisation, modification of residual stresses or of innate properties) and gradual damage accumulation are important, which is entirely inconsistent with the conditions of the laboratory work in (ii). In addition, it is thought that subtle differences in processing conditions have a significant effect (e.g. different manufacturers' apparently similar products give different results in different environments).It is evident from the above that there is room for a materials science investigation of processing/composition/heat treatment-microstructure-property relationships but, in contrast to much previous work, focusing on the conditions of importance to the application such as mechanical properties at the temperatures encountered in service (~ 800 C) and cyclic loading. In addition, state-of-the-art electron optical and other characterisation techniques, using Oxford's extensive range of equipment and expertise, will be used to investigate the differences in microstructure caused by processing variations and subsequent heat treatment and deformation. Research Areas: "Manufacturing Technologies" and "Materials Engineering - Ceramics" in the Manufacturing the Future Theme.