Additive Manufacturing of Titanium Alloys

State of the Art, Challenges and Opportunities

Bhaskar Dutta, Francis Froes

• Publisher: Butterworth-Heinemann
• Year: 2016
• ISBN:
  9780128047835
• Topic: Technology & Engineering
• Subtopic: Mining Engineering
• Index: Technology & Engineering

Additive Manufacturing of Titanium Alloys: State of the Art, Challenges and Opportunities provides alternative methods to the conventional approach for the fabrication of the majority of titanium components produced via the cast and wrought technique, a process which involves a considerable amount of expensive machining.

In contrast, the Additive Manufacturing (AM) approach allows very close to final part configuration to be directly fabricated minimizing machining cost, while achieving mechanical properties at least at cast and wrought levels. In addition, the book offers the benefit of significant savings through better material utilization for parts with high buy-to-fly ratios (ratio of initial stock mass to final part mass before and after manufacturing).

As titanium additive manufacturing has attracted considerable attention from both academicians and technologists, and has already led to many applications in aerospace and terrestrial systems, as well as in the medical industry, this book explores the unique shape making capabilities and attractive mechanical properties which make titanium an ideal material for the additive manufacturing industry.

• Includes coverage of the fundamentals of microstructural evolution in titanium alloys
• Introduces readers to the various Additive Manufacturing Technologies, such as Powder Bed Fusion (PBF) and Directed Energy Deposition (DED)
• Looks at the future of Titanium Additive Manufacturing
• Provides a complete review of the science, technology, and applications of Titanium Additive Manufacturing (AM)

Chapter 1

The Additive Manufacturing of Titanium Alloys

Abstract

Titanium alloys are used extensively in both aerospace and terrestrial applications and in medical industry. This chapter gives a number of applications in these areas. This is followed by a detailed account of the cost of titanium components in which it is concluded that a major cost of these components is a result of the high cost of machining titanium, so that any way of reducing the machining by fabricating net or near-net shapes will reduce the cost of titanium parts. Major efforts have been directed to the use of powder metallurgy as one near-net approach, and this book is directed towards one powder metallurgy technique: additive manufacturing (AM). This chapter presents an overview of AM including a history of the evolution of this technique which dates back almost 100 years. The basic concept can be divided into a number of approaches of which four involve metal processing: directed energy deposition, powder bed fusion, sheet lamination, and binder jetting; and only the first three of these four have been used for processing titanium and its alloys.

Keywords

Titanium applications; titanium cost; titanium machining; titanium powder metallurgy; titanium additive manufacturing; titanium additive manufacturing history

Abbreviations and Glossary

3D three dimensional

AM additive manufacturing

CAD computer aided design

DED directed energy deposition

DMD direct metal deposition

DMLS direct metal laser sintering

EBM electron beam melting

GE General Electric Corporation

LENS laser engineered net shaping

PBF powder bed fusion

P/M powder metallurgy

SL stereolithography

1.1 Introduction

1.1.1 Titanium Alloys and Their Importance

Titanium alloys are among the most important of the advanced materials that are key to improved performance in aerospace and terrestrial systems (Figs. 1.1–1.4) and is even finding applications in the cost conscience auto industry.^1–5 These applications result from the excellent combinations of specific mechanical properties (properties normalized by density) and outstanding corrosion behavior^6–11 exhibited by titanium alloys. However, negating its widespread use is the high cost of titanium alloys compared to competing materials (Table 1.1).

Figure 1.1 The Boeing 787 Commercial airplane contains 20% titanium. Source: © The Boeing Company.

Figure 1.2 GE Aviation’s GEnx is an advanced dual rotor, axial flow high bypass gas turbine engine for use on Boeing’s 787 and 747-8 aircraft and features titanium allow compressor blades and disks. Source: GE Aviation.

Figure 1.3 Author Dr. F.H (Sam) Froes is shown in front of The Guggenheim Museum in Bilbao, Northern Spain, which is sheathed with titanium sheet.

Figure 1.4 Titanium is used for a wide variety of items, such as bike frames, hip implants, eyeglass frames, and earrings.

Table 1.1

Cost of Titanium: A Comparison^a

Item	Material ($/lb)
	Steel	Aluminum	Titanium
Ore	0.02	0.01	0.22 (rutile)
Metal	0.10	1.10	5.44
Ingot	0.15	1.15	9.07
Sheet	0.30–0.60	1.00–5.00	15.00–50.00

^a2015 Contract prices. The high cost of titanium compared to aluminum and steel is a result of (a) high extraction costs and (b) high processing costs. The latter relates to the relatively low processing temperatures used for titanium and the conditioning (surface regions contaminated at the processing temperatures, and surface cracks, both of which must be removed) required prior to further fabrication.

The high cost of titanium compared with the other metals shown in Table 1.1 has resulted in the yearly consumptions as shown in Table 1.2.

Table 1.2

Metal Consumption

Structural Metals	Consumption/Year (10^3 Metric Tons)
Ti	50
Steel	700,000
Stainless steel	13,000
Al	25,000

1.1.2 Challenges to Expanding the Scope of Titanium Alloys

In publications over the past few years^1–29 the cost of fabricating various titanium precursors and mill products has been discussed (very recently the price of TiO₂ has risen to US$2.00/lb and TiCl₄ to US$0.55/lb). The cost of extraction is a small fraction of the total cost of a component fabricated by the cast and wrought (ingot metallurgy) approach (Fig. 1.5). To reach a final component, the mill products shown in the figure must be machined, often with very high buy-to-fly ratios (which can reach as high as 40:1). The generally accepted cost of machining a component is that it doubles the cost of the component (with the buy-to-fly ratio being another multiplier in cost per pound), as seen in Fig. 1.6. Fig. 1.7 illustrates how the machining of titanium has evolved, with rough machining showing a much greater improvement than the much more precise and more expensive final machining. Thus, while improvements in the machining of titanium have occurred, anything that can be done to produce a component which is closer to the final configuration will result in a cost reduction—hence the attraction of near-net shape components.

Figure 1.5 Cost of titanium at various stages of a component fabrication.

Figure 1.6 Boeing 787 side-of-body chord, manufacturing cost breakdown. Source: Courtesy of Boeing.

Figure 1.7 A historical perspective of the machining of titanium showing how various advancements have reduced the cost of machining. The light gray region represents the progress in rough machining and the brown(dark gray in print version) region shows how the final (much more precise and therefore costly) machining has evolved. Source: Courtesy of Boeing.

The high cost of conventional titanium components has led to numerous investigations of various potentially...