Elsevier

Surface and Coatings Technology

Volume 206, Issue 6, 15 December 2011, Pages 1120-1129
Surface and Coatings Technology

Deposition of Ti–6Al–4V using laser and wire, part I: Microstructural properties of single beads

https://doi.org/10.1016/j.surfcoat.2011.07.095Get rights and content

Abstract

In this paper, the microstructural characteristics of Ti–6Al–4V single beads and their dependence on process parameters are addressed. Single beads represent the smallest – and therefore fundamental – unit of additive manufactured components. Bead-on-plates and single beads are produced using a 3.5 kW Nd:YAG laser and Ti–6Al–4V wire. Within 71 sets of process parameters laser beam power, welding speed, and wire-feed speed are varied. The microstructures are investigated by light and scanning electron microscopy, and are divided into several zones according to the thermal history underwent. Microstructural differences of the beads are correlated to the process parameters and discussed. The experiments reveal fundamental microstructural and process characteristics which are helpful for the repeatable and predictable manufacturing and understanding of multi-layered components.

Highlights

► Microstructural characteristics of Ti–6Al–4V single beads are investigated ► The Ti–6Al–4V single beads can be divided into five different zones ► Microstructural zones are similar for beads produced with or without wire

Introduction

In the present paper, the microstructural characteristics of Ti–6Al–4V single welding beads and their dependence on the process parameters are addressed. Single beads represent the fundamental unit for producing multi-layered components. Building up components layer by layer is mostly referred to as rapid prototyping, rapid manufacturing, or additive layer manufacturing (abbrev. ALM). Manufacturing near-net-shape components in a layer-by-layer fashion offers a great potential of time and cost savings in comparison to conventional manufacturing technologies. Especially aerospace components that are machined from costly wrought material at a low fly-to-buy ratio represent interesting applications for additive manufacturing. Wire-feed deposition is discussed as a promising technology in this area. To build up components controllably and predictably by numerous beads, and to understand the microstructural and mechanical properties, prior investigations on single beads are helpful which is verified in [1]. Furthermore, single beads provide data for the validation of finite element (FE) simulations. In [2], [3], single beads are used for simulation of an arc beam based wire-feed ALM process. In [4], [5], [6] single beads are used for simulation of a laser beam based powder-feed ALM process. Furthermore, [7] reports that single beads provide data for closed-loop process control to attain consistency of fabricated parts.

Regarding additive layer manufacturing, wire-feed processes have received less attention than powder-bed or powder-feed (also: blown-powder) processes according to [8] and according to worldwide studies reported in [9]. In 1980, early wire-feed ALM activities called Layerglaze™ were reported in [10]. While wire-feed systems have been used for welding purposes, there have been only a few studies on their potential to create 3D objects according to [11].

The increasing market demand for titanium serial production parts has promoted wire-feed processes in recent years, as repeatability, material properties, material usage, possible part size, and building speed have also become issues. In the literature, it is reported that using wire instead of powder feedstock could lead to a higher material quality of the deposited Ti–6Al–4V, specifically high density. This was figured out in an arc beam based process in [12] and in a laser beam based process in [13]. Additionally, [14], [15] reported of reduced contamination by using wire instead of powder feedstock.

Particular research on single beads for additive manufacturing using a laser beam was published in [16] from the University of Nottingham, in [17], [18] from the Fraunhofer Institute for Production Technology and in [19] from the University of Manchester. Research on single beads using an arc beam was published in [20] from the University of Sheffield & AMRC, using an electron beam in [21] from the NASA Langley Research Center, and using cold metal transfer in [22] from the University of Cranfield.

Section snippets

Wire-feed process

A laboratory wire-feed setup was developed and used for basic research in wire-feed ALM. It essentially comprised a Trumpf HLD 3504 Nd:YAG rod laser (diode pumped) with a maximum power of 3.5 kW, a Weldaix wire-feeder and a Kuka KR 100 HA (high accuracy) 6-axis robot. In an open box, which is permanently flooded by argon from its base (design of the box based on [23]), Ti–6Al–4V welding wire with extra low interstitials (ELI grade) is deposited onto a Ti–6Al–4V substrate. An overview and

Morphology and microstructure

Single beads are composed of different microstructural zones, depending on thermal history underwent. The schematic drawings in Fig. 5 were developed based on the thermal modelings of Ti–6Al–4V deposition in [3], [32], the microstructural and thermal modelings in [33], [34], the welding modeling in [35], the pseudo-binary phase diagram (Fig. 4), and microscopy observations. These illustrate the relationship between the peak temperatures underwent and the resulting microstructural zone at

Morphology and microstructure

Grain growth in (laser) weldments, in which a substrate of the same kind is present, is generally dominated by heterogeneous nucleation [53]. The grain structure near the fusion boundary is dominated by epitaxial growth [35]: solidifying crystals at the interface build upon the crystals or grains of the unmelted, solid parent base metal, take up the substrate's crystal or grain structure and orientation, and grow competitively according to [53]. During solidification, grains tend to grow in the

Summary and conclusions

Understanding the microstructure of single beads for characterization of multi-layered components might be as meaningful as understanding the properties of elementary cells for characterization of metals. Therefore, the microstructure of single beads is investigated in this paper. Relationships between the laser beam power, welding speed, wire-feed speed factor and particular microstructural features are determined and discussed. The experiments reveal fundamental microstructural and process

Acknowledgment

The activities at EADS Innovation Works were especially supported by Frank Palm, Achim Schoberth, and Dr. Claudio Dalle Donne.

References (59)

  • W.U.H. Syed et al.

    Appl. Surf. Sci.

    (2005)
  • S.H. Mok et al.

    Surf. Coat. Technol.

    (2008)
  • W.U.H. Syed et al.

    Appl. Surf. Sci.

    (2005)
  • J.D. Kim et al.
  • A. Majorell et al.

    Mater. Sci. Eng. A

    (2002)
  • F. Karimzadeh et al.

    Mater. Sci. Eng. A

    (2006)
  • R. Ding et al.

    Mater. Sci. Eng. A

    (2002)
  • B. Baufeld et al.

    J. Mat. Proc. Techn.

    (2011)
  • L. Thijs et al.

    Acta Materialia

    (2010)
  • E. Akman et al.

    J. Mat. Proc. Techn.

    (2009)
  • X. Wu et al.

    Mater. Des.

    (2002)
  • E. Brandl
    (2010)
  • A. Anca et al.

    Int. J. Numer. Meth. Eng.

    (2010)
  • V.D. Fachinotti et al.
  • N.W. Klingbeil et al.
  • J. Beuth et al.

    JOM

    (2001)
  • P. Nash et al.

    MS&T (Mater. Sci. Technol.)

    (2004)
  • W.J. Seufzer et al.
  • T.T. Wohlers

    Wohlers Report 2010

    (2010)
  • D.B. Snow et al.
  • W.U.H. Syed et al.
  • B. Baufeld et al.

    Mater. Des.

    (2010)
  • S.H. Mok et al.
  • I.R. Pashby et al.
  • C. Ader et al.
  • C. Freyer

    Schichtweises drahtbasiertes Laserauftragschweißen und Fräsen zum Aufbau metallischer Bauteile

    (2007)
  • U. Clemens
  • G. Escobar-Palafox, R. Gault, K. Ridgway, IOP Materials Science and Engineering Journal (in...
  • K.M.B. Taminger et al.
  • Cited by (0)

    View full text