Fundamentals of static crack growth in nickel-based superalloys after friction welding

镍基高温合金摩擦焊后静态裂纹扩展的基础

• 批准号: 2718829
• 金额: --
• 依托单位: University of Birmingham
• 依托单位国家: 英国
• 项目类别: Studentship
• 财政年份: 2021
• 资助国家: 英国
• 起止时间: 2021 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=studentship-2718829
• 关键词: Fundamentals; static; crack; growth; nickel

Turbine sections of jet engines undergo significant and varying stresses, as well as operational temperatures beyond 750 degrees Celsius, requiring the use of materials capable of maintaining their mechanical properties at high temperatures. Nickel based super-alloys are the current material of choice for aeroengine discs, owing to their high resistance to creep, fatigue, and static loading in the temperature regimes required. If friction welding can be used to join discs into a turbine assembly then weight savings can result. Inertia friction welding (IFW) processes are favoured to join these large components as they do not require shielding environments and welding parameters are easily repeatable and controllable. During this process one component is attached to a rotating flywheel while the other is held fixed. The flywheel is rotated to a predetermined angular velocity (and hence energy), and the two components brought into contact under high axial pressure. Rotational energy is converted to heat via friction at the interface, the softened materials are expelled radially from the work-piece as flash, and a bond is formed between two components. IFW produces large changes in microstructure. High heat generation and deformation in the weld region promote dynamic recrystallisation, as well as dissolution of gamma ' precipitates and their subsequent re-precipitation in a much finer distribution. Unfortunately, such microstructures are highly prone to intergranular cracking if given threshold conditions are exceeded. This cracking is so rapid in air that in could jeopardise the integrity of the aero-engine and cannot be allowed to occur. This project will study the fundamentals of this intergranular crack growth mechanism to define limits to ensure cracks cannot grow under in-service conditions.

喷气发动机的涡轮部分承受着巨大和不同的应力，以及超过750摄氏度的工作温度，这要求使用能够在高温下保持其机械性能的材料。镍基高温合金是目前航空发动机盘片的首选材料，因为它在所需的温度范围内具有很高的抗蠕变、抗疲劳和抗静态载荷能力。如果可以使用摩擦焊接将圆盘连接到涡轮机总成中，则可以节省重量。惯性摩擦焊接(IFW)工艺是连接这些大型部件的首选工艺，因为它们不需要保护环境，焊接参数很容易重复和控制。在这个过程中，一个部件被固定在旋转的飞轮上，而另一个部件则固定不动。飞轮被旋转到预定的角速度(因此也就是能量)，两个组件在高轴向压力下接触。转动能通过界面上的摩擦转化为热，软化的材料以闪光的形式径向从工件中排出，两个组件之间形成粘结。IFW在微观结构上产生了很大的变化。焊缝区的高产热率和高变形促进了动态再结晶，以及伽马析出物的溶解和随后的再析出，分布更细小。不幸的是，如果超过给定的阈值条件，这样的微观组织很容易发生晶间开裂。这种破裂在空气中非常迅速，可能会危及航空发动机的完整性，不能允许发生。本项目将研究这种晶间裂纹扩展机制的基本原理，以确定限制，以确保裂纹在使用条件下不会扩展。