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Title: In situ absorptivity measurements of metallic powders during laser powder-bed fusion additive manufacturing

Here, the effective absorptivity of continuous wave 1070 nm laser light has been studied for bare and metal powder-coated discs of 316L stainless steel as well as for aluminum alloy 1100 and tungsten by use of direct calorimetric measurements. After carefully validating the applicability of the method, the effective absorptivity is plotted as a function of incident laser power from 30 up to ≈540 W for scanning speeds of 100, 500 and 1500 mm s –1. The effective absorptivity versus power curves of the bulk materials typically show a slight change in effective absorptivity from 30 W until the onset of the formation of a recoil pressure-induced surface depression. As observed using high-speed video, this change in surface morphology leads to an increase in absorption of the laser light. At the higher powers beyond the keyhole transition, a saturation value is reached for both bare discs and powder-coated disks. For ≈100 μm thick powder layers, the measured absorptivity was found to be two times that of the bare polished discs for low-laser power. There is a sharp decrease when full melting of the powder tracks is achieved, followed by a keyhole-driven increase at higher powers, similar to the bare discmore » case. It is shown that, under conditions associated with laser powder-bed fusion additive manufacturing, absorptivity values can vary greatly, and differ from both powder-layer measurements and liquid metal estimates from the literature.« less
Authors:
 [1] ;  [2] ;  [2] ;  [2]
  1. Technische Univ. Dresden, Dresden (Germany)
  2. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Publication Date:
Report Number(s):
LLNL-JRNL-740801
Journal ID: ISSN 2352-9407
Grant/Contract Number:
AC52-07NA27344; 15-ERD-037
Type:
Published Article
Journal Name:
Applied Materials Today
Additional Journal Information:
Journal Volume: 9; Journal Issue: C; Journal ID: ISSN 2352-9407
Publisher:
Elsevier
Research Org:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org:
USDOE
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; 42 ENGINEERING; 71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; 47 OTHER INSTRUMENTATION; Additive manufacturing; 3D printing; Selective laser melting; Powder bed fusion; Optical absorption; Laser keyhole; Metal powder; Metal liquid absorptivity
OSTI Identifier:
1392171
Alternate Identifier(s):
OSTI ID: 1420283