Powder Metallurgical Processing For Graded Alloy Microstructures

了解微观结构及其对合金性能的影响是冶金加工的关键部分，因为开发人员正在寻找苛刻应用的材料，例如石油和天然气，化学和航空发动机工业。通过添加微量元素和热机械加工，从而控制化学和微观结构以提供所需的好处，已经实现了合金性能的增强，包括钢和镍高温合金。然而，这种添加和加工步骤通常是在大块合金上进行的，通常会导致成品部件的不良成本，因为在无用的地方存在昂贵的元素添加。在添加贵金属（铂、钯、钌等）时尤其如此。这样的问题可以避免，例如，通过沉积表面涂层。然而，在使用环境条件下，薄的表面涂层可能会退化，暴露出未受保护的合金，缩短组件寿命。在这个项目中，我们将研究产生不对称“分级”合金微观结构的途径，以在部件表面提供性能增强，在需要的地方，避免大量添加合金的成本。集中于粉末冶金加工以产生渐变的显微组织，我们将引入贵金属到钢和镍高温合金的表面，研究对显微组织的影响，改性的显微组织与底层基合金的相互作用，在与这些合金的最终用途应用相关的环境条件下的热机械性能和耐腐蚀性。工业合作伙伴庄信万丰和利伯缇粉末金属将与学生密切合作，提供互补的制造和表征设施，从而使成功的学生获得贱金属和含贵金属合金的经验。

The understanding of microstructures and their effect upon alloy properties is a key part of metallurgical processing as developers seek materials for harsh applications such as those found in the oil & gas, chemical and aeroengine industries. Enhancement of alloy performance has been achieved for ranges of alloys, including steels and nickel superalloys, by addition of minor elements and thermomechanical processing, thereby manipulating the chemistries and microstructures to provide desired benefits. However, such additions and processing steps are generally performed on bulk alloys, often resulting in undesirable costs in finished components arising from the presence of expensive elemental additions in areas where they serve no purpose. This is particularly the case with additions of precious metals (platinum, palladium, ruthenium etc.). Such issues can be circumvented, for example, by deposition of surface coatings. However, thin surface coatings can be subject to degradation by in-use environmental conditions, exposing the underlying unprotected alloy and shortening component lifetime.In this project we will examine routes for generating asymmetric "graded" alloy microstructures to provide property enhancement at the surface of components, where they are needed, avoiding the cost of bulk alloying additions. Concentrating upon powder metallurgical processing to generate the graded microstructures, we will introduce precious metals into the surfaces of steels and nickel superalloys, examining the effect upon the microstructures, the interactions of the modified microstructures with the underlying base alloys, thermomechanical properties and corrosion resistance under environmental conditions relevant to the end-use applications of those alloys. The industrial partners, Johnson Matthey and Liberty Powder Metals, will work closely with the student to provide complementary manufacturing and characterization facilities, thereby allowing the successful student to gain experience of both base metal and precious metal-containing alloys.