Elsevier

Scripta Materialia

Volume 43, Issue 4, 28 July 2000, Pages 299-305
Scripta Materialia

The effect of laser power and traverse speed on microstructure, porosity, and build height in laser-deposited Ti-6Al-4V

https://doi.org/10.1016/S1359-6462(00)00408-5Get rights and content

Introduction

Laser forming is a solid-freeform-fabrication method which can be used to manufacture solid metallic components directly from CAD files. During laser forming, powder is fed into a melt pool which is produced by a sharply-focused laser beam. Parts are built in a layer-by-layer fashion by rastering the laser and powder source across the substrate. Laser forming has many potential applications, including production of functional prototypes, short-run component fabrication, component repair, and fabrication of functionally-graded materials.

Laser forming is particularly attractive for the fabrication of titanium aerospace components because it can greatly reduce the buy-to-fly ratio and lead time for production, two factors which impact cost. Thus, a number of recent efforts have been undertaken to develop titanium laser-forming processes 1, 2, 3. Much of the focus of this prior research has been on equipment development and mechanical property measurements 1, 2. Acceptable processing parameters have been determined largely through trial-and-error approaches. On the other hand, only limited work has been done to establish the relationship between process parameters and the structure of deposits. Such an understanding is critical for both process control and process design. A preliminary attempt to correlate process parameters to the structure of Ti-6Al-4V deposits has been reported by Brice, et al. (3). They investigated the effect of laser power, traverse speed, stand-off distance (laser focus), hatch spacing (line overlap), layer thickness, and powder flow rate on build height and deposit porosity using a screening factorial experiment. They found that build height tends to depend on the contributions of single factors, while deposit porosity depends greatly on the interactions between factors.

The work reported here complements and extends that of Brice, et al. (3). The overall objective was to establish the effect of laser power, traverse speed, and substrate thickness on porosity, build height, and the microstructure (e.g., grain size) of laser-deposited Ti-6Al-4V. For this purpose, a laboratory-scale system was used to conduct a design-of-experiments (DOE) series of trials. The results established the importance of individual process parameters as well as incident energy (∼power divided by traverse speed).

Section snippets

Materials and procedures

The materials used in this investigation consisted of gas-atomized prealloyed Ti-6Al-4V powder made by Crucible Research and two lots of hot-rolled Ti-6Al-4V plate, each having an equiaxed alpha microstructure. The powder had a composition (in weight percent) of 6.29 aluminum, 3.93 vanadium, 0.099 oxygen, 0.0059 hydrogen, 0.009 nitrogen, 0.042 carbon, 0.041 iron, balance titanium and mesh size of −100, +325 (particle sizes between 45 and 150 μm). The thinner Ti-6Al-4V plate (2.90-mm thick) had

Results and discussion

The experimental results are presented and discussed below in sections dealing with macrostructure/microstructure, porosity, and build height.

Summary and conclusions

The effect of process variables and substrate thickness on macrostructure, microstructure, porosity, and build height of laser-deposited Ti-6Al-4V was established using a Laser Engineered Net Shaping (LENS™) system. From this work, the following conclusions were drawn:

  • 1.

    Laser deposition of Ti-6Al-4V is characterized by high temperature gradients and high cooling rates that give rise to columnar microstructures and very fine transformed microstructures. The width of the columnar grains decreases

Acknowledgements

This work was conducted as part of the in-house research activities of the Processing Science Group of the Air Force Research Laboratory’s Materials and Manufacturing Directorate. The support and encouragement of the Laboratory management and the Air Force Office of Scientific Research (Dr. S. Wu, program manager) are gratefully acknowledged. The assistance of Optomec Design Co. (J. Bullen, system operator) in fabricating the deposits and M. Luce in preparing the metallographic specimens is

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References (4)

  • J. T. Schriempf, E. J. Whitney, P. A. Blomquist, and F. G. Arcella, Advances in Powder Metallurgy and Particulate...
  • D.M. Keicher et al.
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