Titanium and Titanium Alloys Properties ME 296T Fall 2016 Ghazwan Al qaraghuli Ahmed Kadhim Nestor Ramos

Outline  Physical Properties of Titanium  Microstructure Phases and Properties  Heat Treatments and Ageing  Titanium Alloy Application  Casting Vs Forging  Titanium Alloys in Elevated temperature  Titanium Alloys in Jet Engine  Titanium Alloys Mechanical Properties  Fatigue Resistance

Introduction  Ti not found in its free pure metal form in nature but as oxides, ilmenite (FeTiO3) and rutile (TiO2) is called Commercial pure (CP-Ti).  (CP-Ti) contains elemental titanium plus some amount of impurities such as Nitrogen (N), Hydrogen (H), Oxygen (O), and Iron (Fe). FeTiO3 TiO2

Physical Properties of Titanium  Titanium alloys are usually divided into three categories: alpha (α ), alpha-beta (α+β) and beta (β).  Pure titanium has hexagonal close packed structure (hcp) in Low or room Temperature and is body-centered cubic (bcc) High temperature (882).

Microstructure Phases and Properties  Commercially pure (CP) titanium alpha and near alpha titanium alloys - Generally non-heat treatable and hard to weald - Medium strength, good creep strength, good corrosion resistance  Alpha-beta titanium alloys - Heat treatable, good forming properties - Medium to high strength, good creep strength excellent ability to be forge.  Beta titanium alloys - Heat treatable and readily formable - Very high strength, low ductility Microstructure for Ti alloy

Heat Treatments and Ageing There are four common heat treatments used for Ti-6A-4V: 1. Mill anneal (MA or A) -- this is the most common heat treatment. 2. Re- crystallize anneal (RA) -- this is a more damage tolerant heat treatment condition. 3. Beta anneal (BA) -- this is used with both the standard and ELI grades. For maximum damage tolerance properties. 4. Solution treated and aged (STA) -- provides the maximum strength, but full hardenability is limited to about 25 mm

Microstructure Phases and Properties  Near α alloys contain α-phase and usually less than 10% of β phase and has good creep resistance.  The β phase improves the strength and workability of the alloys.  (α + β ) alloy promotes equilibrium between higher strength of β alloys and creep resistance of α alloys.

Heat Treatments and Ageing Heat Treatment and elements effect for each phase (a) α phase and β stabilizer (b) β phase and α stabilizer

Composition and Applications of α+β titanium Alloys

Titanium Alloy Application  Titanium alloys are becoming a more common replacement to Ni super alloys in aircraft because of their high-strength to weight ratio.  In aircraft engines there are several applications for Titanium alloy (fans and compressor parts ) because of higher temperatures.  Forgings and heat-treatment made titanium alloys have various characterization.  Fatigue resistance of titanium after heat treatment and aging is greater than that of aluminum or steel.  Good workability  Good fabrication ability

Ti- Alloy(α+β) Properties after Heat Treatment and Aging

Casting Vs Forging Forging  Forged alloy is stronger and more ductile than its cast equivalent in the unexposed condition.  Forged having significantly higher strength with both the UTS and stress value. Casting Casting found extensive application  Reduce the microstructuring cycle cost and time.  Acceptable quality and and strength level.  Lower weight and part count.  Eliminating weld and associated preps.

Titanium Alloys in Elevated temperature  Most of the engine parts which are exposed to higher temperatures are usually made of titanium alloys.  Purpose  Light weight material with high strength.  Thousands of operating hours at temperatures up to (1100 °C).  High mechanical stresses due to high rotational speeds and large aerodynamic forces.  Longer Operating Lifetime.  Time, temperature and stress dependent on effects such as creep, stress rupture, and high- and low-cycle fatigue.  Corrosion/oxidation resistance. Distribute Titanium alloys in Jet engine vs temperature

Cold Section Components  Typical Alloys: Ti-6Al- 4V&Ti6246  Use for Fan disks/blade Hot section components  Typical Alloy : Ti 834  Use for compressor disks Titanium Alloys in Jet Engine

Titanium Alloys Mechanical Properties

Ti-834 ( 5.8Al - 4Sn - 3.5Zr - 0.7Nb - 0.5Mo Si C ) increased tensile strength and creep resistance up to 600°C together with improved fatigue strength. low coefficient of expansion High temperature resistance ( ) °C. High melting point of from (1500 to1735) °C.. High resistant for (fatigue, High Temperature ).

Ti 6Al-4V  Used for low pressure environments (fan).  High-cycle fatigue static and high reliability is required for the rotating disks.  increases substantially with increases strain and with increasing strain rate,but decreases with increasing temperature.  Good creep resistant,High yield strength.  High Stiffness and High Density.  High Strength.  Low Thermal conductivity.  Fatigue endurance.  High rotation with high speed. Ti6246  High fatigue properties and improved creep resistance over Ti6-4,Use For mid- pressure compressor disks.  High fatigue strength and excellent toughness.

Alpha-Alloys- Timetal 834  Creep deformation- 600C  Low to medium strength  Good notch toughness  Well ductility  Mechanical properties at cryogenic temperatures  Highest corrosion resistance  Optimum high temperature creep resistance  Oxidation resistance  Silicon

Improve alpha- alloys  Longer time at the solution heat temperature ( minutes)  Ageing treatment is increased  Add Silicon  For example-Ti 834-ageing treatment- a fine dispersion of (Ti5) Si3, Zr5 Si3 improves its creep properties.  It helps by precipitate out of the solid solution at dislocation sites during deformation.  Precipitation amount-Ageing cycle

Silicon-The Great Direct correlation-% of Si and Creep Resistance Higher % Si→ σ UT →Elongation (%) Higher % Si →Creep resistance

Example- Titanium 17 Double Solution Treatment Acicular alpha phase Forging Low Temperatures (below 450), Statics

Alpha-Beta Alloys  Alpha-beta strength  Heat Treatment and Aging  Least Creep Resistant  Heavy duty purposes (Higher Yield Strengths)  Maximum operated temperature under creep conditions normally is c.  Near alpha alloys heat treated in the alpha-beta phase field °C  Near alpha alloys heat treated in the beta phase field. 600°C.

Fatigue Resistance  Cycle at high Temperatures →Low silicon → rapid cooling = Cracking.  For the higher silicon content alloy, many more cracks were present in the scale, and the scale was observed to be much more porous.  LCF life depending on the the grain size and microstructure and heat treatment.  (α+β) alloy in α stabilizer has less LCF in room temperature, This reduction in fatigue life is due to enhanced planarity of slip resulting from shearing of the phase precipitates.

Fatigue Resistance  In beta titanium, 3wt%Si can be dissolved at the eutectic temperature, 1339 °C. At 865 °C, the eutectic transformation β+α Ti3Si occurs.  For the higher silicon content alloy, many more cracks were present in the scale, and the scale was observed to be much more porous

Summary  Titanium alloy is one of the most used metals in jet engines due to its strength properties to weight ratio  Titanium properties vary by heat treatment or element components

References Smith, W.F., Structure and properties of engineering alloys, second edition, 1993, McGraw-Hill, ISBN PROPERTIES AND APPLICATIONS OF TITANIUM ALLOYS: A BRIEF REVIEW C. Veiga1, J.P. Davim2 and A.J.R. Loureiro3 PRreovp. Aerdtive.s Mantedra. Sppcil.ic3a2ti(o2n0s1o2f)t1it3a3n-iu1m48 Aircraft Gas Turbine Engines Operation, Components & Systems (Jet Propulsion) (Jet Rocked Propulsion) by J. VennardJ. Vennard [3]Development of a High Temperature Titanium Alloy for Gas Turbine Applications byGeraint Rhys Watkins p An overview on the use of titanium in the aerospace industry by R.R. Boyer IATA The IATA Technology Roadmap Report June 2009 Advances in Gas Turbine Technology Edited by Dr. Ernesto Benini Titanium and Titanium Alloys: Fundamentals and Applications Christoph Leyens (Editor), Manfred Peters (Editor) 2003 p 20Christoph LeyensManfred Peters Materials properties handbook : titanium alloys Author: Rodney Boyer; Gerhard Welsch; E W Collings; p440 Cyclic oxidation behavior of aluminide coatings on Ti-base alloy IMI-834 at 750 °C by D.K. Das, Z. Alam