Astm stp 432 1968

APPLICATIONS RELATED PHENOMENA IN TITANIUM ALLOYS A symposium presented at a meeting of Committee B-10 on Reactive & Refractory Metals and Alloys AMERICAN SOCIETY FOR TESTING AND MATERIALS Los Angeles, Calif., 18-19 April, 1967 ASTM SPECIAL TECHNICAL PUBLICATION NO 432 List price $20.00; 30 per cent discount to members ~ published by the AMERICAN SOCIETY FOR TESTING AND MATERIALS 1916 Race Street, Philadelphia, Pa 19103 1968 Library of Congress Catalog Card Number: 68-18768 (~) BY AMERICAN SOCIETY FOR TESTING AND MATERIALS NOTE The Society is not responsible, as a body, for the statements and opinions advanced in this publication Printed in Baltimore, Md March, 1968 Foreword The Symposium on Applications Related Phenomena in Titanium Alloys was presented 18-19 April 1967 in Los Angeles, Calif ASTM Committee B-10 on Reactive and Refractory Metals and Alloys sponsored the symposium Hans Conrad, University of Kentucky, was the symposium chairman It was divided into four sessions, and presiding as chairmen of these sessions were Dr Conrad; R I Jaffee, Battelle Memorial Institute; H P Kessler, Reactive Metals, Inc.; and W W Minkler, Titanium Metals Corporation of America Related ASTM Publications New Structural Materials for Aerospace Vehicles, STP 379 (1965), $6.00 Stress-Corrosion Cracking of Titanium, STP 397 (1966), $14.00 Structural Fatigue in Aircraft, STP 404 (1966), $18.50 Plain Strain Crack Toughness Testing of High Strength Metallic Materials, STP 410 (1967), $5.50 Contents Introduction Fracture Toughness and Notch Strength Source of Fracture Toughness: The Relation Between Klc and the Ordinary Tensile Properties of M e t a l s - - c T HAHN AND A R ROSENFIELD A Review of Factors Influencing the Crack Tolerance of Titanium Alloys J L SHANNON, JR., AND W F BROWN, JR Structural Ductility of High Strength Titanium Alloys RALPH PAPIRNO 33 64 Toughness of Two-Phase 6A1-4V Titanium Microstructures w w GERBERICH AND G S BAKER Relation of Strength and Toughness to Fine Structures in a Beta Titanium Alloy B R B A N E R J E E , J J H A U S E R , A N D J M CAPENOS Plane Strain Fracture Toughness and Mechanical Properties of 5A12.5Sn E L I and Commercial Titanium Alloys at Room and Cryogenic Temperatures c M C A R M A N A N D J M K A T L I N 80 100 124 Fracture Toughness in Aqueous Saline Environments Metallurgical and Mechanical Aspects of the Sea-Water Stress Corrosion of Titanium I R L A N E A N D J L C A V A L L A R O The Influence of Composition and Heat Treatment on the AqueousStress Corrosion of T i t a n i u m - - s R S E A G L E , R R S E E L E Y , A N D G S H A L L 147 170 Effects of Heat Treating Environmental Conditions on the Stress-Corrosion Cracking Resistance of Several Titanium A l l o y s - - o G HOWE A N D R ]' G O O D E 189 Environmental Related Phenomena The Initiation of Hot-Salt Stress Corrosion Cracking of Titanium A1loys s P RIDEOUT Crevice Corrosion of Titanium J D JACKSONAND W K BOYD Biaxial Properties of Titanium Alloys at Cryogenic T e m p e r a t u r e s - s F FREDERICKAND D L CORN Texture Strengthening and Fracture Toughness of Titanium Alloy Sheet at Room and Cryogenic Temperatures T L SULLIVAN 205 218 227 236 Low Cycle Fatigue and Wear Effects of a 3.5 Per Cent Sodium Chloride Aqueous Saline Environment on the Fatigue Crack Propagation Characteristics of Titanium Alloys T W CROOKER AND E A LANCE Lubricants and Wear Coatings for T i t a n i u m - - s j KOSTMAN Surface Treatment of Ti-6A1-4V for Impact-Fatigue and Wear Resistance R D W E L T Z I N A N D G K O V E S 251 268 283 STP432-EB/Mar 1968 Introduction The use of titanium alloys in aerospace and other systems has experienced a rapid increase in the past several years This increased application has revealed that titanium alloys exhibit certain behavior characteristics which can lead to serious consequences if not given proper consideration Some of the more important phenomena related to these characteristics are fracture toughness, stress-corrosion (aqueous and hot salt), crevice corrosion, hydrogen effects, low-cycle fatigue, and wear These are the topics covered in this volume Recognizing the importance of keeping the engineer informed on research under way on such problems, the joint ASTM-ASME Committee on Effect of Temperature on the Properties of Metals sponsored a symposium on "Stress Corrosion Cracking in Titanium Alloys" at the Fall Meeting of the ASTM in Seattle, Washington, on and 2, Nov., 1965 The success of this meeting prompted the sponsoring committee to recommend a follow-up symposium to be held within one to two years on related subjects in titanium alloys ASTM Committee B-10, at its regular meeting on 3, Nov., 1965, acted on this recommendation and offered to sponsor such a symposium, since titanium alloys are within its scope It was subsequently decided to cover a broad range of applications related phenomena rather than limit the symposium to stress-corrosion This broader subject matter, therefore, was taken as the theme for the present symposium Most of the papers presented at the symposium are found in this volume They represent both survey papers by invited speakers and submitted papers of recent work, the combination giving the latest results and thinking on the topics covered One can conclude from these papers that, although the mechanisms associated with the discussed applications related phenomena are still not well understood, there is sufficient information to indicate that they not offer severe limitations to the continued and increased use of titanium alloys Although the papers in this volume are directed principally to the practicing metallurgist and design engineer, they provide a good back1 Copyright9 1968 by ASTM International www.astm.org APPLICATIONSRELATED PHENOMENA IN TITANIUM ALLOYS ground for the more basic oriented materials scientist who wishes to investigate the detailed atomic mechanisms associated with applications related phenomena in titanium alloys Hans Conrad Chairman, Department of Metallurgical Engineering, Universityof Kentucky, Lexington, Ky.; symposiumchairman Fracture Toughness and Notch Strength G T H a h n ~ a n d A R R o s e n f i e l d ~ Sources of Fracture Toughness: The Relation Between and the Ordinary Tensile Properties of Metals REFERENCE: Hahn, G T and Rosenfield, A R., "Sources of Fracture Toughness: The Relation between K~0 and the Ordinary Tensile Properties of Metals," Applications Related Phenomena in Titanium Alloys, ASTM STP 432, American Society for Testing and Materials, 1968, pp 5-32 ABSTRACT: This paper examines crack extension from a metallurgical standpoint Stress and strain intensification at the crack tip and the basic flow and fracture properties of the material are considered Insights derived from etchpitting experiments are reviewed These reveal the two characteristic types of local yielding: (1) plane strain or "hinge-type" relaxation and (2) plane stress or through-the-thickness relaxation Two simplified elastic-plastic treatments that model plane strain and plane stress are identified They offer approximate equations connecting K (the stress intensity parameter) with the plastic zone size and the crack-tip displacement, which are in good accord with experiment They also help to define limiting conditions for plane strain and plane stress A method of relating the crack-tip displacement to the peak strain is described, and this is combined with a critical strain criterion for ductile fracture In this way, the plane strain fracture toughness parameter K~o is formulated in terms of ordinary tensile properties: KI~ = "v/~EYn~g* (E is the modulus, Y the yield stress, n the strain hardening exponent, and g* the true strain at fracture of a smooth tensile bar) This expression is shown to be in good accord with available data on a variety of titanium, aluminum, and steel alloys Since the influence of composition and heat treatment on tensile properties is already established in many cases, the tensile properties can now serve as a link between fracture toughness and the backlog of metallurgical experience This possibility is demonstrated for Type 4340 steel heat treated to different strength levels KEY WORDS: crack extension, fracture toughness, plastic flow, tensile prop- erties, testing, metals, ductility, crack-tip displacement, stress gradient, strain hardening I r w i n ' s concept of fracture toughness has been the subject of m a n y papers a n d seminars Ways of m e a s u r i n g K~o a n d K~ a n d the factors that correct for e n d effects a n d special shapes are finding their way into the literature [1].~ However, virtually n o t h i n g has been said a b o u t the origins Metal Science Group, Battelle Memorial Institute, Columbus Laboratories, Colum_ bus, Ohio 2The italic numbers in brackets refer to the list of references appended to this paper Copyright9 1968 by ASTM International www.astm.org WELTZIN AND KOVES ON SURFACE TREATMENT OF Ti-6AI-4V 285 FIG Impact-fatigue testing apparatus ( X The arrow points to the area of contact between the stud and the striker The same arrangement was used in con]unction with a calibrated microscope to measure impact wear In the first phase of the development project, five different treatments were tried Three of them oxidizing, boriding, and nitriding created a very hard but thin surface compound layer, while two other treatments resulted in the diffusion of chromium and copper respectively to provide a not-so-hard but deeper and more stable surface layer Two of these treatments were quickly abandoned boriding, due to its extreme 286 APPLICATIONSRELATED PHENOMENA IN TITANIUM ALLOYS brittleness, and the copper diffusion because it did not result in any significant increase of hardness In the second phase of the project the remaining treatments were further refined, and the two treatments with the most promising properties were thoroughly tested for impact-fatigue and wear resistance These treatments were: (1) a diffused chromium treatment, and (2) a combination of diffused chromium and a surface nitriding treatment The diffused chromium treatment produced a layer approximately FIG Optical-Jractograph oJ Jatigue Jailed impact specimen On the leJt is the tenon portion, on the right head portion oJ the specimen I cycle , ~1 TIME FIG -Stress pattern applied on specimen during te,~'ting 0.005 in (0.127 mm) thick with a peak hardness about 150 to 200 Knoop units above that of the fully heat treated base alloy The combination chromium diffusion nitriding treatment produced, in addition, a thin but very hard (approximately 1000 Knoop units) compound layer on the surface For comparison, more conventional oxide and nitride surface layers were also tested Table summarizes typical properties of all surface layers Impact-Fatigue Testing The impact-fatigue testing was performed on an experimental arrange- WELTZIN AND KOVES ON SURFACE TREATMENT OF T3-6AI-4V 287 ment originally devised by Koves and later used by Weltzin and Koves The basic tool of this apparatus was a Wiedemann-Baldwin SF-01-U ~ universal fatigue testing machine For this machine, a fixture was designed such that a dynamic, cyclic impact load could be applied to the test specimen Figure is a drawing of the test specimen used in this testing The holding fixture for the stud and the striking head through which the impact load is applied are shown mounted on the fatigue machine in Fig In these experiments the specimen was held by the head and struck on the tenon Failure, thereby, occurred at the deliberately introduced notch due to the change of cross section of the stud The impact-fatigue experiments consisted of dynamically applying a load of predetermined magnitude to the stud and recording the results as stress applied versus the number of cycles to failure The fatigue strength was determined for 107 cycles, at which point testing was halted A photograph of a typical impact-fatigue failed specimen is shown in Fig The loading pattern in this impact-fatigue testing is illustrated in Fig There is no preload present on the specimen, and the loading is unidirectional, with load applied during one half of a complete cycle The calculation of the stress applied to the cylindrical stud during one loading cycle is derived in the Appendix The equation resulting from this calculation is S = 1180F where F = applied impact load imposed on the fatigue specimen To correctly interpret the data resulting from these impact-fatigue tests, the load must be accurately determined The impact load applied by the fatigue machine used in these experiments resulted from the motion of an eccentric rotating weight The load applied by this rotating weight is calibrated for fatigue testing where the oscillating platform is connected to the seismically isolated table by the fatigue specimen To this, we determined the displacement of the stud associated with a given eccentric weight setting We then measured the static load needed to achieve the same displacement This calibration resulted in a determination that the actual applied load on the stud was approximately three times greater than that indicated by the eccentric weight The calculation of applied stress was based on the assumption that no areas of localized high stresses are present In this testing, a stress concentrator was deliberately introduced (that is, 0.010-in or 0.254-mm max break) The localization of high stresses can be expressed by a theoretical stress concentration factor, Kt The value of Kt for a given Koves, G., "The Applicability of AISI C-1213 Free Machining Steel to Complex Fatigue-Shock-Wear Load," Transactions, American Institute of Mining, Metallurgical, and Petroleum Engineers, Vol 230, Feb 1964, p 58 5Trademark of Wiedemann Div., Warner and Swasey Co., King of Prussia, Pa 288 APPLICATIONSRELATED PHENOMENA IN TITANIUM ALLOYS loading condition and notch geometry is easily determined using the data given in the book of stress concentration design factors by Peterson% The effect of a notch on the fatigue strength of a component varies considerably with notch geometry and material The effect of a notch is usually less than one might expect from the value of K~ A scale of notch sensitivity, which is related to the degree to which the theoretical effect is obtained, may be defined as Ks q-Kt where: q = notch sensitivity factor, KI = fatigue notch factor = fatigue strength of unnotched specimen/ fatigue strength of notched specimen, and K~ = theoretical stress concentration factor Using the data available in Peterson, the effect of the deliberately introduced stress raiser, for Ti-6A1-4V with no surface treatment and in the solution treated and aged condition, is expressed by g~ = 2.06 q = 0.35 A compilation of Kt and q for all the surface treatment conditions studied is given in Table T A B L E - - E f f e c t o f the stress c o n c e n t r a t o r on the notch sensitivity o f surface t r e a t e d T i - A I - V titanium alloys ~, b Surface Treatment Fatigue Strength psi kgf/mm2 Ky q Untreated Sandblasted Nitrided 73 000 94 000 45 000 51.0 66.0 31.5 1.37 1.06 2.22 0.35 0.056 I Oxidized 35 000 24.5 2.86 Relative Notch Sensitivity moderate low fully n o t c h e d specimen fully n o t c h e d specimen D i f f u s e d c h r o m e -t- n i trided D i f f u s e d c h r o m e -t- pickle D i f f u s e d c h r o m e (no pickle) 40 000 28.0 2.50 fully notched specimen 94 0013 66.0 1.06 0.095 low 57 000 40.0 1.75 0.71 high K t = 2.06 b U n n o t c h e d b e n d i n g f a t i g u e s t r e n g t h = 100,000 psi (70.0 k g f / m m ) Wear Testing Two types of wear tests were used to determine the effectiveness of the surface treatment procedures in improving wear resistance The first P e t e r s o n , R E., Stress Concentration Design Factors, Wiley, N e w York, 1965 WELTZIN AND KOVES ON SURFACE TREATMENT OF TI-6AI-4V 289 provided a measure of resistance to sliding abrasive wear, the second to wear due to repeated impact The sliding or abrasive wear was performed using the apparatus shown in Fig This test consisted of abrading a case-hardened steel disk (solid arrow) against the treated titanium specimen (hollow arrow) at a fixed speed of 3400 rpm The load applied at the end of the lever arm was adjusted so that Hertz Contact stresses of 20,000 and 10,000 psi (14.0 and 7.0 kgf/mm2), respectively, were obtained The rate of wear was FIG Sliding abrasive wear testing apparatus The photo on the right shows an overall view of the tester The left photo shows in detail the case-hardened disk (white arrow) and the tested specimen (hollow arrow) The contact stress between specimen and disk is determined by the amount of weight at the end of the lever arm determined by the total weight loss of the specimen measured at intervals of No discernible loss of weight of the case-hardened disks was obtained Resistance of the various treatments to wear due to impact loading was determined by the impact-fatigue apparatus shown in Fig and discussed previously This test involved impact-fatigue loading a heattreated stud at a stress (20,000 psi or 14.0 k g f / m m 2) such that fatigue failure would be avoided up to 107 cycles At intervals of a given number of loading cycles, we determined the wear on the tenon of the stud impacted by the striking head of the oscillating platen, using a calibrated 290 APPLICATIONS RELATED PHENOMENA IN TITANIUM ALLOYS t Diffused Chrome t Sondb)osted Pickled 0.05 and 0.1,5rail ~,oo \ ==,~o \ _oo ,oo I- ~.:.,.,, ooo0,, o_~176176176 I 108 104 I0 e I08 IOt 108 Number of Cycles 0I0 ~ 10' 10`5 ' IO' s 10Jr 10P8 Number of Cycles Untreated 9~150 ~-.~ ,,.ooo0s, Diffused Chrome t 150 o~176176 I- \~.~.=-,~,.ooo0s, -" -~,n ~oI- I- IOs 104 10`5 IOs I07 108 Number of Cycles OloSi Nitride ~ o~176176 r 50 ~- \ O[ I05 ~150 ~ ~,~176 tgoo _ I_ , F _S.=25,000 psi , , , I I I to e io 's ior io o/ , i 01/0s t04 ~ t05 ~ iO~e t0~r i0e Number of Cycles I , i Annealed / -r\ 100 ~ s.=35,ooo0s, , IOs 104 IOs 10e 107 I0 e Number of Cycles "~ 150 L Oxide Diffused Chrome +Nitride 0.05 end 0.15 roll 150 ~'~176~ 104 105 I0e 107 108 Number of Cycles \ r to Number of Cycles t ~150 t F.S.= 57,000 psi ~ ~oI e 50~ | i i0 s i04 F.S.= 27,000psi I I i i iOs IO6 107 i0 e Number of Cycles FIG 6~Fatigue curves ]or sur/ace treatments o/ Ti-6.4l-4V measuring stage We plotted as total wear versus the n u m b e r of loading cycles for constant impact stress Impact-Fatigue Testing Results The impact-fatigue testing data were recorded as applied impact stress versus the n u m b e r of cycles of failure, that is, in the standard S - N curve form T h e fatigue curves are given in Fig T h e impact-fatigue strength WELTZIN AND KOVES ON SURFACE TREATMENT OF Ti-6AI-4V 291 at 107 cycles for Ti-6A1-4V in the solution treated and aged condition, with no surface treatment, was 73,000 psi (51 kgf/mm2) The impactfatigue strength was increased by the diffused chrome plus pickle surface treatment procedure, and by abrasive blasting of the surface Each procedure resulted in a fatigue strength of 94,000 psi (66 kgf/mm2) This was an increase of almost 30 per cent and restored the fatigue Sondblosted Untreated ?o ioo ioo = ~ 75 J ~ so ~ 2s I- ,"olook | I0 15 20 Time (rain) Nitride ~ T5 = so 7sf ~ so 25 ]r 25 ~ 0 m I i i i ii I0 15 20 25 Time (rain) Diffused Chrome A ~ ~ I00 I ~0 _ I00 jo 75 Jo 75 50 ~ 50 ~ o p -[ Nitride I0 15 20 Time (rain) xide _ ,oo o ~o I0 5 ~ I0 15 20 Time (rain) FIG - - A b r a s i v e wear 10,000 psi of surface I0 15 20 Time (rain) Diffused Chrome Pickle,0 rail I I0 15 20 Time (rain) treated Ti-6AI-4V Hertz contact stress = strength to approximately the value for the unnotched condition obtained by other investigators All other surface treatment procedures resulted in a marked reduction of the fatigue strength The fatigue strength ranged from 57,000 psi (40 kgf/mm 2) for the diffused chrome (no pickle) surface treatment, to 35,000 psi (24.5 kgf/mm 2) for the oxided surface A fatigue curve was also generated for Ti-6A1-4V in the annealed condition, in order to determine if the lower strength might result in a tougher, more impact-fatigue resistant material The fatigue strength obtained for 292 APPLICATIONSRELATED PHENOMENA IN TITANIUM ALLOYS this modification was 27,000 psi (19 kgf/mm2), only one third that of the Ti-6A1-4V in the solution treated and aged (STA) condition An interesting result of the impact fatigue testing is the beneficial effect of a pickling treatment on the diffused chrome treated material prior to aging at 1000 F (538 C) When identical treatment procedures were used to prepare different chrome surface treated specimens, except for pickling one batch of specimens prior to aging, the pickled specimens gave an increase of the fatigue strength to 94,000 psi (66 k~f/mm2), Diffused Diffused Chrome Chrome Pickled I 0.15 mi~ 9r w tOO NO Plcklel0.OSml I ~ ~ o IO0 *O -J c 5oli _; z5 25 o v- 0 I l I I I I0 15 20 25 ~ Time (rain} I t I0 15 20 Time (rain) Diffused Chrome ~o N o P|cklt, O i fflit }OC 75 g~c 25 O o v- 0 I / I IO 15 i 20 "fi me {rain) FIG (Cont.) while the specimens not pickled exhibited a fatigue strength reduction to 57,000 psi (40 kgf/mm2) Wear Resistance Testing Results The wear resistance of the surface treatments of Ti-6A1-4V was studied with two types of wear tests The first determined the surface treatment resistance to sliding abrasive wear; the second provided a measure of the surface resistance to impact wear Figures and and Table present the results of the sliding abrasive wear study; Fig and Table the results of the impact-wear investigation The sliding abrasive wear tests described earlier were performed at Hertz Contact stresses (HCS) of 10,000 psi (7.0 kgf/mm 2) (Fig 7) and Untreated To I 0 o I ~, Sondblosfed wE) 50 ~ 75 ~ 50 25 ~ a5 75 o _1 o "6 t- o I 0 ;g ,ooI I I ~- o I I0 15 Time (rain) Nitride ~rc ,0 I0 15 20 Time (rain) 25 Oxide I00 75 o ~ 100 5o 9= 5C 25 ~ 25 o ~ I0 15 20 Time (rain) -I 75 I0 15 20 Time (min) Diffused Chrome Pickled,0.05roll T(~ I00 ~ = 75 50 ~- I0 15 20 Time (rain) ~ 25 I00 ~ 75 o I r q'lo I00 I I o I - I I0 15 20 Time (rain) 10 15 20 Time (rain) 25 Diffused Chrome ,o ~ 50 ~ z5 ;o A q.o= Diffused Chrome Pi9 0.15rail I00 J y= 50 ~" z5 25 i0 / Diffused Chroine -{-Nitride To I00 o J 0 NO Ploldet 0.05 roll f J I I I 10 15 20 Time (min) Diffused Chrome No Pi9 O.15mil _1 ~, 50 N 25 o I0 15 20 Time (rain) FIG - - A b r a s i v e wear o f surface treated T i - A I - V H e r t z contact stress -20,000 psi 293 294 APPLICATIONSRELATED PHENOMENA IN TITANIUM ALLOYS 20,000 psi (14.0 k g f / m m 2) (Fig 8) The nitride and oxide surface treatments, which resulted in the greatest reduction of the impact fatigue strength, provided improved resistance to sliding wear The duplex diffused chrome + nitride treatment provided improved wear resistance for a short time (HCS = 20,000 psi) (14.0 k g f / m m 2) and then degraded to a greater sliding wear rate The diffused chrome surface treatment procedures resulted in degraded sliding wear resistance, with one exception The diffused chrome treatment obtained by diffusing 0.05-mil (0.00127 mm) chrome plate into Ti-6A1-4V, solution treated, pickling, and finally aging, provided improved sliding wear resistance This treatment also produced improved fatigue life and excellent surface appearance As a general conclusion, the harder, more notch-sensitive surface treatTABLE Total wear under sliding abrasive wear conditions for various surface treatments o f Ti-6AI-4V S T A Surface Treatment Condition Total Wear, g, after 20 min, HCS = 10,000 psi or 7.0 kgf/mm~ Nitride Oxide 0.17 X 10-4 Sandblasted 0.20 No treatment 0.20 Diffused chrome q- nitride 0.32 Diffused chrome (0.05 ml or 0.00127 mm) pickle 0.22 Diffused chrome (0.15 ml or 0.00371 mm) pickle 0.42 Diffused chrome (0.05 ml or 0.00127 mm) no pickle 0.27 Diffused chrome (0.15 ml or 0.00371 mm) no pickle 0.52 Total Wear, g, after 20 min, HCS = 20,000 psi or 14.0 kgf/mm~ Fatigue Strength psi kgf/mm~ 0.23 X 10-4 0.30 0.64 0.64 0.70 45 000 35 000 94 000 73 000 40 000 31.5 24.5 66.0 51.0 28.0 0.32 94 000 66.0 0.74 94 000 66.0 0.45 57 000 40.0 O 64 57 000 40.0 ment provides improved resistance to sliding wear, but at the same time results in decreased impact-fatigue life Table lists the relative wear rates for the various surface treatments under abrasive sliding wear conditions The impact wear test data are given in Fig 9, with a compilation of total wear at 10 cycles in Table In this type of wear condition improvement was obtained with three surface conditions, notably the abrasive blasted which also improved fatigue strength In general, the harder surface treatments (that is, oxide and nitride) had a very high impact wear rate compared to untreated Ti-6A1-4V STA The combined results of the wear tests on the surface treated Ti6A1-4V shows that the surface treatment best for resistance to sliding wear is also the worst for resistance to impact wear The impact-fatigue testing did not detect any difference resulting from the thickness of the WELTZIN AND KOVES O N SURFACE TREATMENT OF Ti-6AI-4V ~,o Untreated 2.0! "2 2.0 ~o ~- Sondblosted 1.5 g ,~ Lo ~= 1.0 lS io s I I I | I io e ios ios io7 =oe Io Io" Ios Number of Cycles ioe ioT io e Number of Cycles 2.0 2.0 Oxide So m == 1.5 i t 1.5 b "; Lo ~6 Jr J= u=.5 1.0 o JO3 I io" I l@ I ioe I # I I ~ lee Io" Diffused Chrome + N i t r i o e , 0.05 I lee of Cycles 1.5 t.o "g o i io s io io5 loe io~ toe I I sos Io" sos Number of Cycles ~ 2.0 I Id Diffused Chrome +Nitride, O.lfi rail -2 2.0 roll 1.5 "6 I sos Number Number of Cycles 2,0 i so5 I I I sos io~ soe Number of Cycles Diffused Chrome "~ 2.0 L ~o pickledI O.05m|l Diffused Chrome No P|r O.05mil ~= 1.5 o 1.0 == Q c ~ I I I I I Io' Io~ Ioe ;d' Ioe Number of Cyctes i ;os Io~ Io~ Number Ios d of Cycles FIG - - m p a c t wear on sur]ace treated T i - A l - g - Ioe 295 296 APPLICATIONS RELATED PHENOMENA IN TITANIUM ALLOYS T A B L E - - T o t a l wear after 106 impact cycles at an operating stress o f 20,000 psi (14 kgf/mm*) Impact Wear Surface T r e a t m e n t Condition Sandblasted Diffused chrome -4- nitride (0.05mil or 0.00127 m m chrome) Diffused c h r o m e (0.05-mil or 0.0127 m m chrome) None Diffused chrome -4- nitride (0.15rail or 0.00371 mm chrome) Diffused c h r o m e § pickle (0.05rail or 0.00127 m m chrome) Oxide Nitride Fatigue Strength in mm psi kgf/mm2 0.170 X 10-8 0.0043 94 000 66.0 0.220 0.0056 40 000 28.0 0.300 0.520 0.0076 0.0153 57 000 73 000 40.0 51.0 0.780 0.0229 40 000 28.0 0.950 1.68 2.08 0.0249 0.0426 0.0528 94 000 35 000 45 000 66.0 24.5 31.5 T A B L E Relative performance o f surface treatment as determined by impact-fatigue, sliding abrasive wear, and impact wear tests Surface Treatment Impact-Fatigue Abrasive Wear (HCS = 20,000 psi or 14 k g f / m m 2) Impact Wear No t r e a t m e n t A b r a s i v e blasted Nitride Oxide Diffused chrome + nitride (0.05-rail or 0.00127 m m chrome) Diffused chrome -t- nitride (0.15-mil or 0.00371 m m chrome) Diffused chrome-pickle (0.05 ml or 0.00127 ram) Diffused chrome-pickle (0.15 ml or 0.00371 mm) Diffused c h r o m e (0.05 ml or 0.00127 ram) Diffused chrome (0.15 ml or 0.00371 mm) good excellent poor poor poor poor good good fair good poor poor poor poor good poor poor poor excellent good poor excellent poor fair fair good fair poor c h r o m i u m p l a t e d i f f u s e d i n t o t h e t i t a n i u m A n effect o f t h e o r i g i n a l d e p t h o f c h r o m e p l a t e is s e e n f o r b o t h t h e d i f f u s e d c h r o m e a n d d i f f u s e d c h r o m e p l u s n i t r i d e i n w e a r t e s t i n g T h e effect of t h e d e p t h o f o r i g i n a l c h r o m e plate and the pickling treatment was variable, resulting in either an increased or decreased wear resistance, depending on the treatment proced u r e a n d t y p e o f w e a r test A p e r f o r m a n c e r a t i n g s c a l e o f t h e v a r i o u s s u r f a c e t r e a t m e n t s h a s b e e n e s t a b l i s h e d i n T a b l e Conclusion The results of the various tests indicate that for a complex impactf a t i g u e - w e a r l o a d , s i m u l t a n e o u s o p t i m i z a t i o n o f all c h a r a c t e r i s t i c s i n t h e WELTZINAND KOVESON SURFACETREATMENTOF Ti-6AI-4V 297 Ti-6AI-4V alloy cannot be achieved Nevertheless, several combinations of improved properties are available, depending on the basic condition of the alloy and the surface treatment used The design engineer must evaluate the service requirements of a given component and decide on the most important functional property He then can select a treatment which will provide maximum performance for that characteristic and maintain fair-to-good properties in the other needed areas Optimum combinations for many applications can be obtained using this procedure APPENDIX Calculation of Applied Impact Stress Calculation of the stress applied to the cylindrical stud during one loading cycle was determined as follows: As the plate on the oscillating platform (see Fig 2) hits the specimen with a force F, the force creates a bending moment M= ~ _ _ ~ _ Ft (1) _ h r -"0.0955in h=O.O?9 in F I G l(P Relationships used in calculating morimum stress applied to specimens in impactffatigue testing where l = bending lever arm This causes a maximum stress in the outer fibers of the specimen Smax- Mh I where: I = moment of inertia, and h = one-half distance between parallel fiats of specimen tenon (2) 298 APPLiCATiONS RELATED PHENOMENA IN TITANIUM ALLOYS Dimensional quantities used in calculating the stress in the specimen are indicated in Fig 10 The m o m e n t of inertia for a specimen of this configuration is x = r~4 c h (2c _ r 2) (3) As r ~ = c = h ~ and sin/3 = h / r T h e n the relation for I m a y be simplified to I - r4~3 h ( r _ 2h 2) ( r _ h~)1/2 (4) and for the specimen used h = 0.079 in a n d r = 0.0935 in h = 2.0 rnm a n d r = 2.38 m m Therefore, I= 0.458 • 10 -4 i n ? 1= 16mm (5) Substituting Eq into Eq 2, S- Flh 0.458 X 10 -4 S = llSOF, psi _ F ( ) 0.079 0.458 )< 10 S = 2.19F k g f / m m where F i s the applied impact load imposed on the fatigue specimen (6) THIS PUBLICATION is one of many issued by the American Society for Testing and Materials in connection with its work of promoting knowledge of the properties of materials and developing standard specifications and tests for materials Much of the data result from the-voluntary contributions of many of the country's leading technical authorities from industry, scientific agencies, and government Over the years the Society has published many technical symposiums, reports, and special books These may consist of a series of technical papers, reports by the ASTM technical committees, or compilations of data developed in special Society groups with many organizations cooperating A list of ASTM publications and information on the work of the Society will be furnished on request