An investigation in to the effects of recycling of Ti-6Al-4V powders used within selective laser melting

O'Leary, Richard 2015. An investigation in to the effects of recycling of Ti-6Al-4V powders used within selective laser melting. MPhil Thesis, Cardiff University. Item availability restricted.

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Abstract

This report details a systematic study into the effects of recycling of Ti-6Al-4V powders used within Selective Laser Melting. Five identical test builds were produced with a variety of test pieces in order to ascertain any effect of changes in powder characteristics observed on mechanical, chemical and metallurgical properties of laser melted parts. Testing included tensile testing, fatigue testing, chemical composition testing and porosity testing. A quantity of Grade 23 Ti-6Al-4V powder was taken from a single manufacturing batch and run through the SLM process five times. Powder samples were taken from the initial manufacture’s batch, and from within the build chamber at the end of each build, as well as post sieving of the powder from each build. The powders were subjected to Particle Size Distribution analysis, chemical composition analysis and imaged under Scanning Electron Microscope. The purpose of this was to determine the effect of repeated recycling on their PSD range, chemical composition and morphology. The effect of recycling on powder characteristics was shown to be an increase in the number of larger particles contained within the population, and a reduction in the number of fine particles. Repeated recycling was shown to have a statistically significant effect on values of Dx(10), Dx(50) and Dx(90), which all increased. These changes in powder characteristics within the powder population were shown to have no statistically significant effect on the mechanical properties of parts produced. There was no effect observed on UTS, Yield Strength, Percentage Elongation or Fatigue Strength for parts produced in the five builds. It was not possible to say that this trend would continue with indefinite recycling. The effect of position within the build chamber in which the parts were built was shown to be strongly significant, with large variation in mechanical properties of parts produced in different positions. Porosity analysis showed an increase in porosity for parts which exhibited the worst mechanical performance when compared to that of those with the best mechanical performance. Through chemical composition testing, there was shown to be a large increase in the percentage by weight of oxygen contained within laser melted parts when compared to the powder that was used to manufacture them. These parts contained a percentage by mass of oxygen that was outside the allowable limit stipulated for Grade 23 Ti-6Al-4V parts. It was not possible to say whether the level of oxygen absorption varied with build position.

Item Type:	Thesis (MPhil)
Date Type:	Completion
Status:	Unpublished
Schools:	Engineering
Subjects:	T Technology > TJ Mechanical engineering and machinery
Uncontrolled Keywords:	Selective Laser Melting (SLM); Powder Recycling; Chemical and Metallurgical Properties of SLM Parts.
Date of First Compliant Deposit:	31 May 2016
Last Modified:	13 Apr 2022 15:43
URI:	https://orca.cardiff.ac.uk/id/eprint/91255

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