Start date and planned duration: January 2019, 36 months
Objectives
- Understand, characterise and control the causes of defect populations in parts manufactured using selective laser melting (SLM), and assess their effect on mechanical performance.
- Develop the methodology for optimisation of SLM process parameter selection and demonstrate this on three selected alloy systems – nickel Alloy 718, Ti-6Al-4V and AlSi10Mg alloys.
- Generate statistically significant data on the fatigue performance of each of these alloy systems using the optimised parameters developed, for material with and without treatment bv hot isostatic press (HIP).
- Generate comparative data to quantify the deviations in fatigue performance resulting from factors including different powders sources (Ti-6Al-4V), powder recycling through SLM (alloy yet to be determined) and powder storage conditions (AlSi10Mg).
- Make available to industry a database of fatigue performance data for use in the design of SLM components, as well as revised evidential guidelines on powder handling / management and the efficacy of HIPing of SLM components.
Project Outline
The key to achieving full density, and consequent enhanced mechanical performance, in components produced via SLM is to fully understand the sources of the porosity and to control these rigorously and methodically. Porosity in an as-built component is a consequence of the quality of the powder fed into the process and the choice of SLM process parameters selected for the particular machine in question.
TWI (working with Lloyd’s Register) has developed a rigorous methodology for optimisation of SLM process parameters – laser power, scanning speed, hatch distance, and layer thickness. This project will apply the lessons learned from 316L stainless steel and extend the methodology to the optimisation of parameters for other materials key to industrial needs: Ni alloy 718, Ti-6Al-4V and AlSi10Mg. The methodology will also be developed to take scanning strategy into account and to demonstrate transferability of results between different SLM equipment.
In terms of the powder material fed into the SLM process, defects can arise from entrapped gas porosity within powder particles from the atomisation process used to produce them, and/or additional contamination of powder through improper storage or excessive multiple re-use. The project will examine the influence of each of these factors on the resultant development of porosity within builds and the consequent effect on fatigue performance.
At each stage of this work it is important that a statistically significant number of specimens is built and tested to fully establish the fatigue performance, under both low cycle and high cycle fatigue conditions, including quantification of the degree of scatter in the results. Baseline tensile properties will also be established. Where appropriate, specimens will be tested in both HIPed and non-HIPed conditions in order to quantify any additional improvement.
Guidelines will be drawn up addressing the issues of powder selection, handling and recycling as well as the recommended methodology for SLM parameter optimisation.
Industry Sectors
Benefits to Industry
Industry will benefit by having access to specific knowledge and a database of fatigue performance, enabling evidence-based decisions in the development of new applications for SLM components. Industry will also be able to make an informed choice, backed by evidence, with regard to the requirement for HIPing for their particular application requirements. The results of the project will also feed into ongoing certification work being undertaken by TWI and Lloyd’s Register; the guidelines produced, with evidence to support them, will fill a gap where currently no ASTM or other recognised standards exist.
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