NSIRC252 PhD Studentship - Extreme High-speed Laser (EHLA) Coatings

Protecting components against wear and corrosion has no trivial solution, with standard coating processes, such as hard chrome plating or thermal spraying having their drawbacks in terms of health and environmental concerns, coating quality or process efficiency.

Laser metal deposition (LMD) could be an attractive alternative, offering high integrity coating potential with significant material performance benefits over conventional processes with which it competes. LMD is already used in a limited number of cases, however its principal drawbacks are its slow coverage rate and the relatively high heat that has to be used, which can be an issue in some crack-sensitive materials.

This project proposes to develop a fundamental understanding for TWI of a completely new LMD technology, using a recently developed extreme high-speed laser (EHLA) nozzle design manufactured by Fraunhofer ILT. This understanding will start from 15 years of existing LMD processing expertise at TWI, and apply the experience gained to a number of relevant industrial needs.

The EHLA nozzle is capable of applying coatings up to in 300 µm thickness, and can also work at traverse speeds of up to 100 m/min. This represents an entirely new capability, and takes LMD from coverage rates of ~10-40 cm2/min to rates possibly up to 250 cm2/min. This is achieved by introducing the powder stream into the line of the laser beam, causing it to melt prior to reaching the melt pool, thus reducing the laser energy input into the substrate component, which in turn reduces dilution.

Project Outline
TWI has recently acquired the UK’s first dedicated EHLA system. The PhD will focus on experimental research with this new and exciting system.

A number of different coating materials could be examined by this PhD, but as a first application, nickel-chromium based alloys would be targeted, these representing an important coating family for exploitation using EHLA LMD. However, in all cases, there is a significant gap in the understanding of the effects of processing parameters, powder composition and powder particle size distribution on the maximum speed of deposition that can be achieved, and the quality of the deposited material (dilution, HAZ, porosity, surface quality and material properties) that results. PhD work in this area can help to develop validated and robust EHLA process parameter set(s) for these alloys for industrial application (e.g. stem coatings in turbine shafts).

This PhD will be aligned with a 3-year core research programme starting in January 2020 on EHLA coatings. For this programme of work there will a number of industrial mentors to steer applications and materials.

Objectives
A developed fundamental understanding of the EHLA process and the relationships between process inputs and process outputs.
A developed knowhow in thin-coating capability to state-of-the-art level relevant to industrial applications.
Strengthened expertise in LMD, with a UK-unique new offering in the form of an EHLA system.
Application driven benchmarking of EHLA coatings against end-use quality and performance requirements, with reference to competing manufacturing methods.

Approach Overview
The PhD student will lead the fundamental developments of TWI’s understanding in this novel coating technique through work across four areas:
• A state-of-the-art and literature review.
• Carrying out iterative series of processing trials, to develop a number of application-specific deposition parameter sets for different materials.
• Relating the qualities and properties of the coatings deposited, through detailed characterisation and testing of selected results of the EHLA trials.
• Manufacturing of example demonstrator components, through which the developed EHLA process can also be benchmarked against competing processes.

About NSIRC
NSIRC is a state-of-the-art postgraduate engineering facility established and managed by structural integrity specialist TWI, working closely with lead academic partner Brunel University, the universities of Cambridge, Manchester, Loughborough, Birmingham, Leicester and a number of leading industrial partners. NSIRC aims to deliver cutting edge research and highly qualified personnel to its key industrial partners.

Candidate Requirements
Candidates should have a degree at 2.1 minimum in the subject of additive manufacturing, material science, mechanical engineering, chemistry, or an equivalent relevant subject. Overseas degree in (academic and industry requirements) Overseas applicants should also submit IELTS results (minimum 6.5) if applicable.