TWI Industrial Member Report Summary 922/2009
By C Y Kong, M Doré, L Zhang and L S Smith
Direct metal laser deposition (DMLD) is an increasingly attractive additive manufacturing/repair route that can offer advantages over other processes, such as those based on arc welding. In particular, heat input and distortion are low and the sophisticated systems to accurately control the processing head to build up a deposit on the workpiece give superb flexibility. For nickel alloys, the low heat input can prevent liquation cracking in the service exposed substrate and provide an enabling technology for significant life extension of damaged parts which might otherwise require replacement.
The main barrier to the wider implementation of laser-based additive manufacture, is that engineers cannot easily design parts that are produced using these techniques because the mechanical properties and potential performance of the deposited metal are not fully understood. DMLD will only achieve its full potential when a link between the process parameters used, the microstructure created and the properties of the deposit is established, thereby creating the necessary information for part design.
The current programme is intended to address these needs and provide some basic data of relevance to the aerospace sector on the performance of DMLD deposits. Alloy 718 is a well-established material, with applications in many areas of modern and established aeroengine design. Furthermore alloy 718 components can be very large and thus some of the greatest savings (through repair or additive manufacture) can be made when adopting DMLD for this or similar materials. Manufacturers have established considerable data sets on the performance of this material and it is typically the baseline from which other polycrystalline alloys are judged. For these reasons, alloy 718 was chosen for the present study. The deposits were given a direct double age heat treatment following welding, representative of either additive manufacture onto solution annealed material (prior to ageing the entire structure) or repair followed by direct ageing.
- Assess the performance of direct metal laser deposits, as would be employed for additive manufacture or repair, and establish any links between performance and observed weld quality and detailed microstructure.
- Establish quantitative data that can be employed for modelling of the microstructural development of direct metal laser repair deposits.
- Provide guidance for an effective strategy for DMLD additive manufacture and repair of alloy 718 and similar materials.