Diffusion Bonding is a solid state process of joining metallic or non-metallic materials and is achieved by the atomic diffusion at the joint interface without any significant deformation of the components being joined together. The result is a very clean homogenous joint, formed with minimal distortion and with a joint tensile strength comparable to that of the parent materials. Diffusion Bonding is a particularly advantageous technique for joining dissimilar metals/materials and thin coated metal layers, because unlike the more usual welding processes the parent materials to be joined are not melted and re-solidified as part of the conventional diffusion bonding process. The technique has found a number of applications in the aerospace industry, including the joining of liquid rocket combustion chamber sections, and aircraft jet engine nacelle frames that require high manufacturing dimensional tolerances. In the electronics and instrumentation industry, diffusion bonding is used in high value precision components such as optical elements for ultra-high vacuum units. Diffusion bonding is also used to manufacture heat exchangers.
The quality and soundness of diffusion bonds are usually evaluated by metallographic techniques and destructive testing techniques such as shear strength/tensile strength on a statistical basis. This is because there is currently no commercially available NDT technique that can be used to reliably detect defects of the required dimensions and size in diffusion bonded joints during manufacture or in-service. The project partners believe that a suitable validated NDT technique and system needs to be developed that will meet appropriate detection criteria, which can be commercialised and made available to industry. The project will develop an advanced ultrasonic phased array ultrasonic testing (PAUT) technique and with optimised transducer parameters for different material combinations and algorithms for imaging of the ultrasonic signals that will then be processed through ‘automated defect recognition’ (ADR) software to provide an accurate and repeatable defect evaluation tool.
Approach to market
Commercially, the project will result in a validated ultrasonic NDT system and technique that offers speed, safety and innovation for the testing of diffusion bonds. The BondTest system, and its component parts and software that includes an ‘automated defect recognition’ (ADR) algorithm package, will be sold to product manufacturers who use diffusion bonding welding technology for example inspection/NDT companies, end-user plant operators and their mechanical maintenance companies. The RTOs will be remunerated at competitive market rates and the SMEs will retain full rights and ownership of the BondTest project results for their commercial exploitation.