R&D on Composition and Processing of Titanium Aluminide Alloys for Turbine Engines

104 Pages·2009·3.64 MB·English

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THIS PAGE IS UNCLASSIFIED
AFWAL-TR-82-4086
R&D ON COMPOSITION AND PROCESSING4
OF TITANIUM ALUMINIDE ALLOYS
FOR TURBINE ENGINES
United Technologies Corporation Pratt & Whitney Aircraft Group
Govomment Products Division
West Palm Beach, Flodda 33402
July 1982
-1 Interim Report for Period October 1980 to January 1982
Distribution limited to government agencies only; contains Test and Evaluation
June 1982: Other requests for this document must be referred to
I, Air Force Weight Aeronautical Laboratyo riesg, Wright-
Patterson Air Force Base, Ohio 45433 .
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Include this notice with any reproduced portion of this document.
MATERIALS LABORATORY
AIR FORCE WRIGHT AERONAUTICAL LABORATORIES
AIR FORCE SYSTEMS COMMAND
WRIGHT-PATTERSON AIR FORCE BASE, OHIO 46433
82 12 13 ()6.L
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invention that may in any way be related thereto.
This technical report has been reviewed and is approved for publication.
4.2 /
/;ARRY LIPS NORMA M. GEYER
Projec Engineer Technical Area Manager
Processing & High Temperature
Materials Branch
Metals & Ceramics Division
FOR T1 C(OEN HW4NER:
'I1ýNRY CV/GRAHAM, Chief
Processing & High Temperature
Materials Branch
Metals & Ceramics Division
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REPORT DOCUMENTATION PAGE READ INSTRUCTIONS
BEFORE COMPLETING FORM
1. REPORT NUMBER 2. OVT ACCESSION NO. 3-RECIPIENT'S CATALOG NUMBER
A.FWAL-TR-82-4086-
4. TITLE (and Subitfle) S TYPE OF REPORT I PERIOO COVEREO
R&D ON COMPOSITION AND PROCESSING OF Interim Technical Report
TITANIUM ALUMINIDE ALLOYS FOR TURBINE October 1980-January 1982
ENGINES PP ERFORMING ORG. REPORT NUMBER
FR- 16259
7. AUTHOR(s) 8 CONTRACT OR GRANT NUMBER(s)
M. J. Blackburn
NI.P . Slmth F33615-80-C-5163
9. PERFORMING ORGANIZATION NAME AND AODRESS 10. PROGRAM ELEMENT. PROJECT. TASK
AREA 6 WORK UNIT NUMBERS
UTC - Pratt & Whitney Aircraft Group
Government Products Division 24200127
West Palm Beac&, FL 33402
III . CONTROLLING OFFICE NAME AND AOODESS 12. REPORT DATE
Materials Laboratory (MLLI) June 1982
Air Force Wright Aeronautical Laboratories 13. NUMBEROF PAGES
Wright-Patterson AFB- Ohio 45433 91
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Distribution limited to U.S. Government agencies only. Test and Evaluation;
June 1982. Other requests for this doc~uent niust be referred to AFWAL/MLLM,
1%PAFB, Ohio 45433
I?. DISTRIBUTION STATEMENT (of the abstract entered in Block 20. It dil.leternt Itrai Report)
IS. SUPPLEMENTARY NOTES
19. KEY WORDS (Continue on #evote#o lde it neceessay and Identify by block numlber)
Titanium Alumninides, Alloy Development, Isothermal Forging, Titanium Ingot
Production, Mechanical Properties, Titanium Alloy Microstructures, Titanium
Machining, Titanium Casting
20. ABSTRACT (Continu ,re an evde aie It n.cee.asv end Identify by block number)
Materials based on the intermetallic phases Ti3Al (a2) and TiAl (y) exhibit
several attractive features that make them candidates for gas turbine engine
applications. Low density, good oxidation resistance and high temperature
strength are such characteristics and could result in substitution for the
nickel alloys currently used for turbine engine components that operate at
internediate temperatures. Basic alloy development studies over the past
eight years have identified the base Ti-Al-Nb-V and Ti-Al-V systems,
DID FjA'r3 1473 EDITION OF I NOV 6S IS OBSOLETE UNCLASSIFIED
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Block 20 (Cont'd.)
respeqtively, ad the most attractive ba'se compositions for the two alloy
S--4ypes- In this current program, one alpha-two and several gamma compositions
were selected, produced as large ingots and isothermally forged. Extensive
mechanical property testing was conducted on these forgings. In addition,
various material processing methods such as casting, rolling, extrusion and
machining were evaluated.
The alpha-two alloy Ti-2SAl-IONb-3V-IMo exhibited the best balance of tensile
and stress-nrpture properties found to date and had a higher elastic modulus.
Beta grain size was shown to have major effects on creep, low cycle fatigue
and fracture toughness. Alloy stability, as measured by post-exposure
tensile ductility, was poor and was tentatively traced to precipitation of
an unidentified phase in the beta. Heat treatment modifications were
suggested to alleviate this problem. Processing studies showed that many
of the methods developed for forging, joining and rolling of conventional
titanium alloys can be applied to the alpha-two alloys.
Screening tests conducted on four gamma alloys did not identify an alloy with
a betteýr property balance than Ti-48AI-lV-.lC which had been evaluated pre-
viously. Properties were more consistent with previous small scale ingots,
although ductility and impact strength were somewhat lower, and quite good
toughness levels were measured. Alloy stability was excellent after exposure
and processing studies establis'ed machining procedures and demonstrated that
the alloy has fair castability.%z-
l ii
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PREFACE
This is an interim Technical Report (PWA Report FR-16259) covering work
performed under Contract F33615-80-C-5163 during the period between
October 1980 and January 1982.
The investigation was conducted by the Commercial Products Division of
Pratt & Whitney Aircraft, East Hartford, Connecticut, under the technical
"direction of Dr. H. A. Lipsitt, AFWAL/MLLM, Wright-Patterson Air Force Base,
Ohio.
Dr. M. J. Blackburn was the Program Manager, Mr. M. P. Smith was the
responsible engineer and Mr. D. R. Haase was the experimental assistant.
Thanks are extended to Ms. Nancy Giampolo for typing and editorial assistance.
• I,
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TABLE OF CONTENTS
SECTION PAGE
I INTRODUCTION 1
II PROGRAM SCOPE AND APPROACH 2
1. Background 2
2. Program Plan 3
3. Alloy and Process Selection - 3
Alpha-Two Alloy
| 4. Alloy and Process Selection - 4
Gamma Alloys
III EXPERIMENTAL DETAILS 7
1. Material Procurement 7
and Processing
a. Large Ingots and Forgings 7
IV RESULTS AND DISCUSSION 20
1. Introduction 20
2. Material Characterization - 20
Alpha-Two Alloy
3. Material Characterization - 44
Gamma Alloys 1-4
a. Screening Tests 44
b. Material Characterization - 48
Ti-48Al-lV-. lC
4. Processing Studies 64
a. Net Shape Gamma Alloy Casting 64
b. Gamma Alloy Machinability 69
c. Forged Alpha-Two Alloy Compressor 82
Blade
d. Alpha-Two Alloy Sheet Analysis 82
V ANALYSIS AND CONCLUSIONS 87
REFERENCES 91
S..V
LIST OF ILLUSTRATIONS
FICURE PACE
1 As-received titanium aluminide ingots supplied 9
by RMI. (a) S/N 20007; (b) left to right, S/N
20008, S/N 20009, S/N 20010, S/N 20011.
2 Pancake forging preforms machined from PRI 10
titanium aluminide ingots a) S/N 20007;
b) S/N 20008; c) S/N 20009; d) S/N 20010;
e) S/N 20011. Note fairly extensive porosity
on gamma alloy ingots (b-e) compared to the
alpha-two alloy a).
Top and bottom riews of as-forged Ti-47A1-2V- 12
2Nb-lMo alloy pancake.
4 ToT, and bottom views of as-forged Ti-47AI-2V 13
al',y pancake.
5 Top and bottom views of as-forged Ti-47A1-2V-.IC 14
alloy pancake.
6 Top and bottom views of as-forged Ti-48A1-lV-.lC is
alloy pancake. Note better die fill and less
cracking.
7 Top and bottom views of as-forged Ti-25AI-10Nb- 16
3V-lMo alloy pancake.
8 Specimen used to measure tensile, creep and low 17
cycle fatigue capability of titanium aluminide
alloy.
9 Specimens used for impact and fracture toughness 18
evaluation of titanium aluminide alloys.
10 Physical property specimens used for titanium 19
aluminide study. a) thermal expansion; b) modulus
of elasticity; c) specific heat; d) conductivity
11 Macro- and microstructure of the forged and heat 21
treated Ti-25A1-l0Nb-3V-lMo pancake forging (a).
The rim, mid-radius and center microstructures are
in b, c and, respectively.
12 Microstructures of various titanium aluminide creep 24
specimens tested at 650C/372 MPa (1200F/S5 ksi).
vi
LIST OF ILLUSTRATIONS (ONT'D.)
FIGUR11 PAGE
13 Macrostructure of as- forged Ti- 25A1-10Nb- 3V- iMo 24
alloy pancake forging. This was forged on iso-
thermal dies at 1120C (20SOF) in one step from
a cast ingot.
14 Macrostructure of Ti-25A.-10Nb-4V pancake forging 25
from a previous program(4). Top, as-conventionally
upset and forged at 1120C (2050F); bottom, heat
treated llS0C (2100F)/l/ + salt quench to 81SC
(ISOOF)/. S/AC.
Is Effect of thermal exposure on hardness of Ti-25A1- 28
l0Nb-3V-Ilo tensile specimens.
16 Surface of exposed Ti-25A1-l0Nb-3V-1Mo alloy tensile 28
specimen showing alpha case contamination, which
has a hardness of DPH 700-800.
17 SEN fractographs of tested Ti-2SA1-1ONb-3V-lMo 29
tensile specimens.
18 General microstructure of Ti-2SA1-l0Nb-3V-lilo 30
alloy thin foils cut from tensile specimens.
19 Enlarged view of Figure 18 showing the relatively 32
"clean" beta phase in the unexposed specimen 2588
and the darkened beta phase with heavy precipi-
tation in the exposed specimen 2933.
20 General microstructure of the unexposed Ti-2SA1- 33
1ONb-3V-lMo tensile specinten 2588 showing spectrum
and composition of alpha-two and beta phase.
21 S/N curve for smooth Ti-2SAl-l0Nb-3V-lMo alloy 36
specimens tested at 650C (1200F).
22 S/N curves for notched Ti-25Al-Nb-3V-lBlo specimens 37
tested at 650C (1200F) based on grain size.
23 Selected notched Ti-25A1-lONb-3V-lMo LCF specimens 38
showing extremes in grain size but similar micro-
structures.
24 Young's modulus of Ti-2SAI-1ONb-3V-lIo alloy specimen 40
vs. temperature.
25 Thermal conductivity of the Ti-25AI-l0Nb-3V-D~o alloy. 42
vii
.. .-...-.- ,---.-
LIST OF ILLUSTRATIONS (CONT'D.)
FIGURE PAGE
26 Enthalpy of the Ti-25A1-lONb-3V-lMo alloy. 42
27 Heat capacity of the Ti-25A1-lONb-3V-lMo alloy. 43
28 Thermal expansion of the Ti-25AI-lONb-3V-lMo alloy. 43
29 Cross sections of tested gamma alloy titanium 46
alum-inide tensile specimens showing internal porosity
(arrow, brackets).
30 Grinding cracks and porosity on thread surface of 47
Ti-48A1-lV-.IC tensile specimen. Right, a cross
section of a thread root on the same specimen
revealing a root crack.
31 Microstructures of Ti-48A1-lV-.IC creep specimens so
showing relative amounts of acicular phase present.
32 Continuous oxide layer formed on Ti-48A1-lV-. lC 53
alloy specimens after a thermal exposure of 500 hours
at 675C (1250F) plus 100 hours at 730C (1350F)
(brackets).
33 Fracture mode in precracked slow bend toughness 56
specimens. Left column, Ti-48Al-lV-.1C; right
column, Ti-25Al-l0Nb-3V-1Mo. Note difference in
grain size.
34 S/N curves for smooth Ti-48AI-IV-. lC LCF specimens 57
drawn to show effect of grain size on 650C (1200F) life.
35 Fracture appearance and microstructures of smooth 58
Ti-48Al-lV-.lC LCF specimens tested at 650C (1200F)
and 344 MPa (50 ksi).
36 Ti-48A!-lV-.lC smooth LCF specimens tested at 650C 59
(1200F) and 344 MPa (50 ksi). Note origins in coarse
grain areas in specimen 3744 (a) and 3749 (b). Fracture
path (c) is basically intergranular.
37 S/N curve for 815C (1500F) notched low cycle fatigue 61
specimens.
38 Young's modulus of the Ti-48A1-lV-.lC alloy. 62
39 Thermal conductivity of the Ti-48Al-lV-.lC alloy. 63
viii