Using Laser Ultrasound to Detect Subsurface Defects in Metal Laser Powder Bed Fusion Components

Sarah Everton,Phill Dickens,Chris Tuck,Ben Dutton

doi:10.1007/s11837-017-2661-7

Abstract

Laser powder bed fusion offers many advantages over conventional manufacturing methods, such as the integration of multiple parts that can result in significant weight-savings. The increased design freedom that layer-wise manufacture allows has also been seen to enhance component performance at little or no added cost. For such benefits to be realized, however, the material quality must first be assured. Laser ultrasonic testing is a noncontact inspection technique that has been proposed as suitable for in situ monitoring of metal additive manufacturing processes. This article explores the current capability of this technique to detect manufactured, subsurface defects in Ti-6Al-4V samples, ex situ. The results are compared with x-ray computed tomography reconstructions and focus variation microscopy. Although laser ultrasound has been used to identify material discontinuities, further work is required before this technique could be implemented in situ.

Highlights

The laser powder bed fusion (PBF) process has a large number of input parameters, many of which are interdependent.[1]
The samples were removed from the build chamber, de-powdered, and sliced from the baseplates by wire electrical discharge machining (EDM)
To visualize the defect zones created, the blocks have been subject to X-ray computed tomography (XCT) using a Nikon MCT225 XCT machine

Summary

Introduction

The laser powder bed fusion (PBF) process has a large number of input parameters, many of which are interdependent.[1] To produce components with sufficient material integrity, an understanding of the effect of changing these parameters is required, and many studies have been undertaken in this area.[2,3] Various ‘‘defects’’ are known to occur during AM processing, the most common of which are pores, inclusions, and cracks.[4]. Porosity is considered significant as pores reduce the effective load-carrying capacity of a material and act as stress concentrators, providing effective crack initiation sites.[5] Pores can be further categorized by size, shape, and content such as ‘‘spherical, gas filled’’;6 ‘‘elongated, powder filled’’;7,8 or ‘‘keyhole’’ pores.[9] Pores can result under a variety of different processing conditions. This approach will be replicated to create zones of intended porosity in samples

Methods

Results

Conclusion