The document discusses the processing of titanium metal from ore. Titanium is refined from rutile ore using the Kroll process, which produces porous titanium sponge. The sponge is purified through vacuum arc remelting and forging, casting, or powder processing to form usable titanium products. Special precautions must be taken when processing titanium to prevent embrittlement from oxygen, nitrogen or other impurities. Heat treating can develop specific microstructures and strengthen alloys like Ti-6Al-4V for applications such as aerospace parts. Joining methods require inert atmospheres and temperature control to avoid cracking or reduced fatigue life in titanium.

1. Presentations for PowerPoint
Metallurgy
Fundamentals
Ferrous and Nonferrous

2. Titanium
Chapter 18

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• Explain how titanium is refined from ore.
• Explain how the strength of titanium is maximized while retaining
ductility.
• Identify the differences in hot-rolling, forging, extruding, casting, and
powder processing titanium compared to steel.
• Describe diffusion bonding and how it affects brazing titanium.
• Explain how chemical milling assists with the finish processing of
titanium.
Learning Objectives

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• Titanium is commonly used in golf clubs, bicycles, and eyeglass
frames.
• Less-visible titanium components include airplane parts, prosthetic
implants, and chemical reaction chambers.
• As a chemical, titanium dioxide has completely replaced lead oxide
for making white paint.
• Titanium alloys are lightweight and can withstand high temperatures
and corrosion.
Introduction

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• Titanium is refined from rutile, a naturally occurring form of TiO2
mined mostly in Australia and South Africa.
• Metallic titanium is produced using the Kroll process.
• Rutile crystals are extracted from ore.
• The crystals are heated with coke and chlorine gas to produce
titanium tetrachloride (TiCl4).
• The TiCl4 is reacted with magnesium metal in a sealed container.
• This reduces TiCl4 to porous titanium metal called “sponge titanium.”
Refining and Processing Titanium

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Sponge Titanium
Bjoern Wylezich/Shutterstock.com

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• The Kroll process was invented by William Kroll in the 1930s and
perfected in the 1940s.
• Method to commercially extract titanium and zirconium
• Kroll moved from Luxembourg to US in 1940 to escape Nazi
Germany.
• His metallurgical knowledge and process aided the Allied war effort.
Kroll Process

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• A new process to refine titanium recently came online.
• FFC Cambridge process produces metal powder directly from
titanium oxide by electrolysis.
• After this or Kroll process, impurities must be removed.
• Gaseous elements oxygen, nitrogen, and hydrogen
• Any remaining magnesium from Kroll process
FFC Cambridge Process

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• In the VAR process, sponge metal is formed into a rough electrode
and remelted in a vacuum remelt furnace.
• An electric arc is struck between titanium electrode and ingot pool.
• This melts tip of electrode and forms a remelt ingot.
• Most volatile elements are released and removed by vacuum pumps.
Vacuum Arc Remelting (VAR) Process

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• Any alloy additions are added and melted
into the ingot.
• Some critical applications require double
and triple remelting.
• Reduces volatile impurities and assures
uniformity.
Vacuum Arc Remelting (VAR)
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• Melting titanium in a vacuum is necessary to remove oxygen.
• Oxygen dissolves in titanium, forming a Ti-O alloy.
• TiO2 particles precipitate during cooling, sharply reducing ductility.
• Dissolved oxygen stabilizes hcp (alpha) phase of titanium, which is
undesirable.
• Alpha phase is harder and lower in ductility.
• It can produce internal cracks during hot work.
Remove Oxygen to Prevent Alpha Phase

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• Nitrogen also dissolves in titanium and has property effects very
similar to oxygen.
• Nitrogen must also be
removed by vacuum remelting.
• Iron is also undesirable in
titanium.
Impurities Affect Strength
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• Ingots as large as 36″ (91 cm) in diameter and up to 15,000 pounds
(6800 kg) are produced by vacuum melting.
• Obtaining sound, homogeneous ingots requires operators’ constant
attention.
• Final ingot can be processed by standard bulk deformation methods
(rolling, forging, or extruding).
• Producing billet, bar, plate, sheet, strip, or tube
Titanium Ingots

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• Titanium pieces must be protected from air during hot work.
• Above 1100°F (600°C), titanium absorbs oxygen and nitrogen, forming
a Ti-O-N alloy layer on the surface, called alpha case.
• Alpha case (hcp structure) has low ductility and will not undergo
phase transition during any heat treatment.
• When cooled, TiO2 and Ti2N particles form in alpha case, making it
brittle and likely to crack during use.
• Alpha case is removed by acid etching or mechanical grinding.
Manufacture of Titanium Products

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• As titanium alloys cool from high-temperature beta to lower-
temperature alpha phases, various ratios of phases develop.
• Some alloys remain entirely beta phase, and some entirely alpha.
• Different processing conditions produce different microstructures
and properties.
• This depends on thermal cycle and hot-working used.
Alpha and Beta Phases in Titanium

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• Above 1400°F (760°C), titanium ingots are easily
rolled.
• Hot-rolling titanium at temperatures just below
beta-alpha transition at 1620°F (882°C) produces
grain refinement.
• Where controlled atmosphere furnaces are
available, plates and bars can be heat-treated to
high strength.
Hot-Rolling Mill Products—Sheet and
Plate
mironov/Shutterstock.com

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• Process procedures strongly affect strength of titanium alloys.
• Small changes in procedures may affect impact and fatigue strength
of components.
• Some titanium alloys are designed to have both alpha and beta
phases at room temperature.
• UNS R56400 (Ti-6Al-4V) is an example, and it requires careful control
of deformation and temperature.
Alpha-Beta Titanium Alloys

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• During titanium forging, oxygen and nitrogen in air react to develop
alpha case.
• A major purpose of forging parts is to obtain metal flow patterns that
increase load capacity.
• Impact strength of titanium landing gear struts is determined by
forging temperature and degree of work in closed die.
• Preheating dies helps maintain workpiece temperature while forging.
Forging

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• Extruding titanium produces long lengths
of seamless pipe, as well as products with
complex cross sections.
• Titanium is extruded at temperatures
where high-temperature beta phase
exists.
• Ensures dynamic recrystallization and
maximizes plasticity
• Billet is heated then covered with molten
glass to extrude it.
Extrusion
Reprinted with Permission from Plymouth Tube Co. (www.plymouth.com)

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• When cold formed, titanium has high
level of springback.
• It must be “overformed” to achieve
design angles.
• Titanium has more springback for
two reasons.
• It has a lower modulus of elasticity.
• It has high yield strength.
Forming Titanium
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• Sometimes titanium is “warm formed” at temperatures below alpha-
beta transformation temperature.
• This reduces springback.
• Titanium’s greater springback is useful for eyeglass frames.
Titanium Warm Forming
CHARMANT USA Inc.

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• When formed slowly at 1562°F (850°C), titanium elongates 200%
(superplasticity).
• Eight times more than typical fully annealed metals
• Occurs because titanium recrystallizes dynamically
• Dislocation tangles never develop; titanium does not work harden.
Superplastic Forming

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• Example:
• Weight is placed on a titanium
sheet.
• This is placed on a die with cavities.
• Entire fixture is placed in vacuum or
inert gas furnace.
• Sheet deforms under load and
forms into die shape in few hours.
Superplastic Forming Example
Solar Atmospheres; Beckwood Press Company

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• Titanium castings may possess the
tensile and creep-rupture strength of
wrought titanium.
• Mold materials are typically graphite.
• Machined from blocks or compacted
from graphite powder
Casting Titanium
Radomir Rezny/Shutterstock.com

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• Cast titanium usually has small shrinkage voids and porosity.
• Cast aerospace parts are routinely hot isostatic pressed (HIP).
• Closes pores and restores fatigue strength
• Castings are placed into HIP chamber for two hours at 1650°F
(900°C).
• Argon atmosphere at 15 ksi (105 MPa) is used.
• About 1000 atmospheres of pressure
Hot Isostatic Pressing

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• Titanium powder can be compacted and sintered to form dense,
near net-shaped parts.
• Thermal processing must be done in vacuum or inert gas
atmosphere.
• Prevents oxygen absorption
• HIP processing achieves full density.
• Results in maximum ductility, yield strength, and impact strength
Titanium Powder Processing

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• Titanium metal powder is a fire hazard.
• It must be stored in flameproof containers.
• Only class D fire extinguisher puts out titanium powder fire.
• Burning titanium removes oxygen from water.
• This releases hydrogen that burns.
• Operations that process titanium powder must have class D fire
extinguishers in all working areas.
Titanium Powder Fire
Safety Note

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• Commercial-purity titanium can be stress relieved or annealed.
• Stress relieving is done at 900°F–1100°F (480°C–595°C).
• Annealing is done at 1200°F–1400°F (650°C–760°C).
• Time depends on how long it takes to heat workpiece’s center.
• Annealing is usually done by air cooling.
• Thin alpha case layer develops and may need to be removed later.
Heat Treatment of Titanium

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Titanium Going in Furnace for Heat
Treatment
mironov/Shutterstock.com

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• A duplex anneal purposely develops a specific ratio of alpha-to-beta
phases in microstructures.
• Improves creep resistance and fracture toughness
• Instructions are different for each alloy and production sequence
and must be followed exactly.
• Vacuum and inert gas furnaces are preferred for high-temperature
thermal cycles of titanium.
• For critical dimensions, hard vacuum is required.
Duplex Anneal (Alpha-Beta Anneal)

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• Ti-6Al-4V is most frequently used titanium alloy.
• It is solutionized, quenched, and aged to improve strength,
toughness, fatigue strength, and impact strength.
• Heated to 1750°F–1775°F (955°C–970°C) for one hour
• Water quenched quickly after removal from furnace
• Aged 4–8 hours at 900°F–1100°F (480°C–595°C)
• Produces microstructure of fine beta particles and alpha matrix
• Typical yield strength is 155 ksi (1069 MPa) with 16.5% elongation.
Precipitation Hardening Titanium Alloys

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• For aerospace parts, furnaces must be
calibrated frequently to meet standards.
• Aging must be higher temperature than
application.
• Compressor blades in jet engines run at or
above 900°F (405°C).
• Blades must be age hardened near upper end
of temperature range.
• Process instructions may be affected by
conditions of application.
Temperature Control of Aging
Chesky/Shutterstock.com; Jonathan Weiss/Shutterstock.com

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• Furnaces must be maintained to achieve uniform temperature within
25°F (14°C) across entire furnace.
• But 25°F (14°C) is entire permitted temperature range for heat-treating
Ti-6Al-4V titanium.
• Technicians and operators must carefully monitor processes.
• Make sure furnace calibrations are current and settings match
planned processing for parts.
Furnace Control
Practical Metallurgy

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• Titanium parts can be joined like many other metals.
• Arc welding, brazing, adhesive bonding, mechanical fastening
• Complex components can also be joined by diffusion bonding.
• Solid-state technique used to join similar and dissimilar metals
• Atoms of two metals diffuse together over time.
Joining Titanium

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• Experienced welders can join titanium using GMAW or GTAW.
• Workpieces must be cleaned thoroughly before welding.
• Inert cover gas of argon or helium is required.
• Supplementary inert cover gas (“trailer”) may be used to protect cooler
areas near welds.
Arc Welding Titanium

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• Welds must be absolutely protected from oxygen and nitrogen.
• Hot metal is embrittled when it absorbs either of these.
• Welding may be done inside controlled atmosphere chambers.
• Electron beam and laser welding are done in a hard vacuum.
Arc Welding Titanium (cont.)

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• Titanium has many useful applications in
chemical process reactors, pressure vessels,
and piping.
• Can withstand high temperatures and
pressures and remains chemically inert
• Titanium is preferred for papermaking using
wet chlorine gas.
• Desalination plants rely heavily on titanium.
Process Equipment
ImagineStock/Shutterstock.com

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• Brazing must minimize air exposure.
• Vacuum brazing is most common method.
• Some braze filler alloys are liquid below beta transformation
temperature for unalloyed titanium.
• Brazing in a vacuum chamber uses filler alloy foil between titanium
pieces at 1290°F (700°C).
• Workpieces keep original microstructure.
• Filler alloy melts and flows into joints.
Brazing Titanium

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• Higher-temperature braze filler alloys
are used where designs require
strength at high temperature.
• Entire assembly is heat-treated to
strengthen it after brazing.
• Achieves maximum strength
High-Temperature Brazing
Seven Cycle, Inc.

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• Braze joints made, then titanium parts
held at 1700°F (925°C)
• Aluminum in joint diffuses into
titanium at that temperature.
• Finished joint is alloyed titanium with
strength equal to parent.
Diffusion Bonding
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• Diffusion bonding and superplastic forming operations can be
combined into one furnace cycle.
• Multiple parts can be joined to form complex shapes.
Diffusion Bonding (cont.)

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• Brazing, diffusion bonding, and superplastic forming of titanium all
require careful monitoring.
• If vacuum chamber develops small leak, oxygen forms brittle alpha
layer on titanium, leading to surface cracks and reduced fatigue life.
• Close temperature control is necessary during long thermal
processing.
• Swings of 35°F (19°C) during superplastic forming change forming
rate, resulting in incomplete or distorted parts.
Maintaining Close Control during Brazing

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• Titanium machining conditions are
similar to stainless steel.
• Titanium can be polished and anodized.
Machining and Finishing
MarinaGrigorivna/Shutterstock.com

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• Chemical milling uses temperature-controlled baths of etching
chemicals consisting of nitric acid and hydrofluoric acid.
• Can remove selected portions of components, reducing weight without
producing scratches or notches
• Can also remove alpha case on mill products and forgings
Chemical Milling

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• Operators must be extremely careful working around hydrofluoric
acid.
• If acid contacts skin, it continues to react until reaching bone.
• Even a small wound may take months to heal.
• Safety kits with HF-neutralizing solutions must be close to any
operation involving this acid.
Hydrofluoric Acid
Safety Note

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• Titanium has excellent corrosion resistance
• Resists seawater, body fluids, fruit juices,
certain acids and bases
• Titanium is biocompatible with living things,
making it useful for many medical
applications.
• Hip and knee implants
• Pacemaker cases
• Dental implants
Corrosion Resistance and
Biocompatibility
Monstar Studio/Shutterstock.com

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• Most common titanium alloy is UNS
R56400 (Ti-6Al-4V).
• Contains 6% aluminum (Al) and 4%
vanadium (V)
• Yield strength is controlled through
heat treatment.
• Prior processing controls grain size.
• Table compares unalloyed grade 2
titanium (UNS R50400) with annealed
and heat-treated Ti-6Al-4V.
Summary of Mechanical Properties
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• Titanium can be recycled to reduce costs and environmental impact.
• Titanium is too costly to use for most consumer products.
• All manufacturers that use titanium recycle scrap.
• Aerospace industry is biggest user of titanium and biggest driver of
titanium recycling.
Recycling Titanium
Sustainable Metallurgy