Ranking the Resistance of Wrought Superalloys to Strain-Age Cracking

Transcription

1 fimn *'* SUPPLEMENT TO THE WELDING JOURNAL, FEBRUARY 2006 Spnsred by the American Welding Sciety and the Welding Research Cuncil Ranking the Resistance f Wrught Superallys t Strain-Age Cracking The cntrlled heat rate test was used t rank the crack resistance f several allys, and a crrelatin between ally perfrmance and chemical cmpsitin was established BY M. D. ROWE ABSTRACT. High-strength, heat-resistant allys are critical cnstructin materials fr mdern gas turbines used in pwer generatin and aviatin applicatins. The use f higher-strength allys has lng been limited by the susceptibility f sme f these allys t strain-age cracking during pstweld heat treatment. N widely accepted test methd exists that prvides an easy and ecnmical methd f ranking the resistance f allys t strain-age cracking. Of the test methds that appear in the literature, the cntrlled heating rate test (CHRT), develped in the 1960s, stands ut because it is simple and ecnmical as well as having been crrelated t restrained weldment test results. In this investigatin, the CHRT was used t rank several cmmercial allys by their resistance t strain-age cracking, and ally perfrmance was crrelated t chemical cmpsitin. Intrductin Strain-age cracking is a prblem that can ccur during pst-fabricatin heat treatment f allys that strengthen by precipitatin f y. Typically, these are nickel-based allys that cntain aluminum and/r titanium, either fr high-temperature strength r xidatin resistance. Cracking can ccur when an ally that cntains /-frming elements in slid slutin is heated thrugh a temperature range in which / precipitates, abut 1100 t 1800T (590 t 980 C). during the pstweld slutin annealing heat treatment. During the precipitatin f /, the ductility f the ally may drp t a very lw level, and cracking can ccur if the ally is subjected t a level f strain that exceeds the available ductility. In a restrained fabricatin, tensile stress develps as a result f the vlume cntractin that is assciated with the frmatin f Y frm slid slutin. M. D. ROWE is with Dept. f Civil Envirnmental Engineering, Michigan Technlgical University, Hughtn, Mich. The prblem is aggravated by a carse grain size, the presence f an xidizing atmsphere, and cnstitutinal liquatin f carbides, which can further degrade ductility (Ref. 1). Cracking is frequently assciated with weldments because f residual stress, grain grwth, cnstitutinal liquatin in the heat-affected zne (HAZ), and the stress cncentratin at the te f the weld. Hwever, cracking can ccur in the unaffected base metal in additin t the weld metal and HAZ. A test methd that is capable f ranking the resistance f allys t strain-age cracking is needed in the develpment f new allys. In rder t accmplish the ally-develpment bjective, it is necessary t cmpare the weldability f newly develped experimental allys t each ther and t existing cmmercial allys. In rder t be effective, the test methd must prduce a quantitative index f weldability, require a minimum f material and labr, and be pssible t implement with readily available and inexpensive equipment. Review f Strain-Age Cracking Test Methds Early investigatrs used the restrained circular patch test t evaluate the resistance f allys t strain-age cracking (Refs. 2, 3). The circular patch test has the advantage f emplying an actual restrained weldment, which is similar t a real fabricatin. Hwever, the test is nly reprducible if the parts KEYWORDS Strain-Age Cracking Superallys CHRT Test Weldability Weldability Test Nickel-Based Allys arc precisely machined and jined with a highly cntrlled, autmated welding prcess (Ref. 4). The restrained weldment test is useful t demnstrate that an ally can be welded, but has many disadvantages as a ranking test. The test requires a large investment f labr and material, many variables are invlved that are difficult t cntrl, the result is scmiquantitative at best, and the level f restraint cannt be varied easily. Sme investigatrs reprted that the level f restraint in a circular patch test is nly sufficient t crack ally in a repair-weld simulatin, but nt in the riginal weld (Refs. 2, 3). A test that cannt crack a susceptible ally such as in a reprducible manner is nt useful in ranking mre-resistant allys. Several investigatrs have used the Gleeble thermmechanical testing apparatus t simulate strain-age cracking (Refs. 5-11). The Gleeble ffers brad flexibility in the thermal cycles and mechanical strain that can be applied, which has led t a wide variety f test methds and specimen gemetries. Many f the Gleeble tests use a rund-bar specimen, which is nt suitable fr testing sheet material. A Gleeble test fr use n sheet material was develped by Naka (Ref. 9). This methd uses a ntched sheet specimen, and allws fr determining the effect f a wide variety f welding r heat treatment thermal cycles n the ductility f varius allys. The varius Gleeble test methds that appear in the literature have each been the subject f nly a single paper and have nt becme widely accepted, therefre the dcumentatin is limited, and the test results have nt yet been crrelated t the behavir f actual restrained weldments. Selectin f the Cntrlled Heating Rate Test (CHRT) Of the test methds that were reviewed, the mst thrughly dcumented and ec- WELDING JOURNAL

2 ffiifi nmical methd appears t be the cntrlled heating rate tensile test (CHRT) develped in the late 1960s (Ref. 1). In the CHRT, a slutin annealed tensin-test specimen is heated at a cntrlled rate t a test temperature in the Yprccipitatin temperature range, then pulled t failure. The test is repeated at varius temperatures ver the / precipitatin temperature range, and the minimum elngatin fr a given ally is taken as an indicatr f susceptibility t strain-age cracking. The test is as ecnmical as a standard tensile test and can be perfrmed n the same equipment. The CHRT differs frm sme ther test methds in that it dcs nt emply a hlding time in the / precipitatin temperature range. The cntinuus heating rate f the CHRT is selected t simulate the heating rate that wuld ccur in pst-weld slutin annealing f a fabricated cmpnent in a batch furnace. In typical fabricatin practice, the welded cmpnent is heated as rapidly as pssible thrugh the y" precipitatin temperature range t the slutin annealing temperature; thus the use f hlding times in the precipitatin temperature range wuld nt be relevant t fabricatin practice. Fawley et al. evaluated several different mechanical tests and fund that the CHRT gave the best crrelatin t the results f highly cntrlled and autmated restrained-circular-patch tests (Ref. 1). The CHRT was cnducted n millannealed material that was nt subjected t welding r t a HAZ thermal cycle. Subjecting the specimen t a weld thermal cycle reduced the measured CHRT ductility, but did nt alter the ranking f the varius heats f Rene 41 ally, thus it was determined that cracking susceptibility was a prperty f the base metal, and that the HAZ thermal cycle was nt a necessary cmpnent f the test. Fawley et al. went n t evaluate the effects f heat treatment and test atmsphere n cracking susceptibility using the CHRT. Testing in an inert atmsphere r vacuum was fund t significantly imprve resistance t cracking. The mst imprtant parameter determining the resistance f varius Rene 41 ally heats t cracking was fund t be grain size. Fawley et al. fund that heats f Rene 41 ally that exhibited greater than % elngatin in the CHRT did nt crack in the circular patch test. The effectiveness f cntrlling grain size and f heat treatment in an inert atmsphere t avid strain-age cracking was later cnfirmed in prductin at Rcketdyne. The CHRT was selected fr this investigatin based n its simplicity and the reprted successful use f this test t quantitatively rank the effectiveness f varius prcessing methds and material variables in preventing strain-age cracking f Rene 41 ally fabricatins. Materials Standard mill prductin material was used fr testing in the frm f in.- (1.6-mm-) thick sheet. Allys and heat numbers are listed in Table 1. Material was tested in the mill-annealed cnditin, the cnditin in which it wuld be purchased and welded by fabricatrs. Grain size and hardness f the as-received material prir t testing are given in Table 2. Standard mill prcessing f and allys invlved a final anneal in air, fllwed by water-spray quench. Standard prcessing f,, and allys invlved a final bright anneal in a hydrgen atmsphere, fllwed by cling in hydrgen, which results in a slwer cling rate than spray quench. The prcessing details fr ally were nt prvided. All specimens were remved in an rientatin transverse t the rlling directin f the sheet. Cntrlled Heating Rate Test (CHRT) Prcedure The CHRT prcedure (Ref. 1) was adapted fr use n a standard tensile test frame with a resistance-heated clamshelltype furnace. The sheet tensile specimen had a reduced sectin measuring in. thick by 0.5 in. wide by 2.25 in. lng (1.6 x 12.7 x 57 mm). Gage marks were placed n the specimen, and then it was laded int the test frame. Specimens had a tendency t break in gage marks placed n the reduced sectin, s elngatin was measured based n gage marks made in the shulders f the test specimen and percent elngatin was calculated based n the adjusted length f the reduced sectin, as described in ASTM Specificatin E Three thermcuples were wired t the test specimen, at the tp, middle, and bttm f the reduced sectin. Table 1 Chemical Cmpsitin f Allys, vvt-% Ally Heat Al i; c Nb ZNJ C Cr Fe M Ni Si Ti Zr Al+Ti + Nb+Ta (at Fractin y' at 500 C('') DUCT(h) %) Ntes: (a) The equilibrium mlar fractin y al 500*C was calculated using Pandat sftware. Fr Ally 7 IS, the fractins J' an.1 Y" we added tgethe (b) DUCT = 25.39&C- 15.4%Si + 299% B FEBRUARY 2006

3 It was necessary t test withut the use f an extensmeter in rder t reduce the thermal mass sufficiently t achieve the desired heating rate. The specimen was heated t 1100 ±3 F (593 ± 1.7*0) in the clamshell furnace and held at that temperature fr 10 min. The three temperature zne cntrls n the furnace were then increased t achieve a unifrm heating rate f 25 t 30 F/ min. until the desired test temperature was reached. Upn reaching the temperature, the three cntrllers were set t hld that temperature during the test, and the specimen was pulled t failure at a cnstant crsshead speed f in./min (1.6 mm/min). The specimen was remved, cled, and the elngatin was measured frm the failed specimen. The yield stress in the CHRT was calculated frm a 0.2% ffset n a lad-displacement curve. Other Tensile Test Methds In additin t the CHRT, three ther tensile-test methds were used fr cmparisn. The ASTM E21 tensile test invlves maintaining the test temperature fr 20 min prir t testing, maintaining a strain rate f 0.005/min t the yield pint, then increasing the crsshead speed t 0.11 in./min t fracture. Tw variatins n the ASTM test were als used, in which the specimen was held at the test temperature fr 5 r 20 min, and the specimen was pulled t failure at a cnstant crsshead speed f in./min. Calculatin f Phase Fractin Diagrams Thermdynamic phase balance calculatins were cnducted using Pandat sftware (v. 5.0), made by CmpuTherm LLC, alng with the Ni-Data (v. 6) database f thermdynamic prperties, made by Thermtech Ltd. Results and Discussin CHRT Results The CHRT results fr the set f cmmercial allys are given in Table 2 and pltted in Fig. 1. Each value in Table 2 represents the average f duplicate tests. The average difference between duplicate values f the CHRT minimum elngatin was 0.5 percentage pints fr the data set in Table 2. Three heats f ally were tested, and these gave the lwest elngatin values in the test prgram at 2 t 3%. Tw heats f ally were tested, giving the nextlwest elngatin values at abut %. ally perfrmed similarly t. The tw heats f ally perfrmed similarly t each ther, but differed frm the ther allys. Ally exhibited a ductility minimum f 7 t 8% near F ( C), then recvered t mre than 50% elngatin at T ( C). Allys with a high fractin f / exhibited lw ductility ver a greater temperature range than ally and thse with a smaller fractin f /, including and allys. Ally is knwn t be relatively weldable cmpared t ther precipitatin-hardcnable allys, but is nt immune t cracking during heat Table 2 Cntrlled Heating Rate Test (CHRT) Results Ally Heat ZNJ2879 ZNJ2879 ZNJ2879 Grain Size (ASTM) 4^ <s Hardness (RB) M 25.9W 25.9M 25.9<i 27.4w 27.4w 27.4=) Test Temp ( F) Test Temp CO 78S 787 AGL Elngatin (%) % Yield Strength (ksi) Ultimate Strength (ksi) (a) Rckwell C scale. WELDING dournal : f

4 .! (! lilllllll 11 i i i g n) 12 w I- 10 z 5 8 I 6 I « g \ \ \ \ X-75\ \ ^ _, V ^ x> PKWti&sjT^. R-4V~^ S 7 Al + Tr + Nb (at%) CHRT Test Temperature ( C) uj I- 10 CE 5 8 i«i * ***"*>* Calculated fractin f Gamma Prime al 500 C Fig. I Cntrlled heating rate test (CHRT) elngatin vs. test temperature fr several cmmercial, wrught superallys. Each symbl represents the average f duplicate tests. Fig. 2 Cn-elatin f CHRT elngatin t ttal ^-frming ally cntent (tp) and t calculated fractin fy (bttm) fr cmmercial wrught superallys. Each symbl represents the average f duplicate tests l 0.30 * 0.25 r Liquid FCC min R" = 0.53 js M*A UaC "A- MO Temperature fc) a / S ASTM R 2 = 0.58 OCHRT 20 min. at T AASTME21 X5 min. at T CHRT R' = Al+Ti+Nb+Ta (at. pet.) BOO Temperature fc) Temperature ('C) Fig. 3 Calculated phase fractin diagrams fr fur allys. Intermetallic phases were suspended in the calculatins t represent the phase mixture that may frm in a shrt-term test, such as the CHRT. Fig. 4 Cmparisn f the ranking given t a set f five allys by the cntrlled heating rate tensile test (CHRT) t the ranking given by ther tensin test methds. Each symbl represents a single test result. All allys were tested at F ( C). Lw R 2 values fr the 20-min and ASTM test methds indicate the lack f a cntinuus trend fr these tw test methds, in cntrast t the CHRT results. treatment. Allys and gave greater elngatin values than the ther allys. 12% and 19% respectively, wing t their lwer fractin f/. Crrelatin f CHRT Results t Chemical Cmpsitin and Calculated Phase Fractins Minimum elngatin values fr the allys crrelated well t the ttal atmic percentage f /-frming elements. The minimum CHRT elngatin als crrelated well t the fractin f / in each ally at 500 C, as shwn in Fig. 2. Calculated fractins f / are given in Table 1. The equilibrium fractin f / was calculated at the relatively lw temperature f 500 C t represent the maximum fractin f / that each ally is capable f frming. The ttal atmic percentage f/-frming elements is cnsidered t be a surrgate fr the maximum fractin f / that is capable f frming in each ally. At the test temperature where the CHRT minimum elngatin ccurred, the equilibrium fractin f / is less than the fractin at 500 C, and the actual fractin present in the ally during the test wuld depend n the kinetics f precipitatin, disslutin, and carsening in each ally. Calculatin f the FEBRUARY 2006

5 I : ; A 0 A * c ra 6.0 I O E : [ <> ""[A : 0 : A * n -'""". « DUCT=25.3*%C-15.4*%Si+299*%B (Thamburaj et al. 1979) B 1.0 : ((grain diameter, mm) A -0.5)+0.7*(DUCT) 8.0 Fig. 5 A C/relatin f CHRT elngatin t the empirical parameter DUCT develped by Thumberaj et al; B crrelatin fchrtelngatin functin f inverse square rt f grain diameter and DUCT scaled by a factr fo. 7. t a Fig. 6 Fracture surface f a ally CHRT specimen tested at the minimum ductility temperature. Light ptical images f the test specimen shwing intergranular cracking. A and B Brittle intergranular and ductile rupture regins n the fracture surface. Secndary electrn images. C intergranular fracture regin; D ductile regin. Fig. 7Fracture surface f a ally CHRT specimen tested at the minimum ductility temperature. Light ptical images f the test specimen shwing intergranular cracking. A and B Brittle intergranular and ductile rupture regins n the fracture surface. Secndary electrn images; C intergranularfractureregin; D ductile regin. Y fractin at 500 C resulted in a better crrelatin with CHRT minimum elngatin than when the fractin f Y was calculated at the test temperature, suggesting that a large supersaturatin, r thermdynamic driving frce, fr precipitatin f Y during the heating phase f the test is an imprtant cntributr t cracking susceptibility. The calculated equilibrium fractin f Y at the test temperature is nt as representative f the cnditin f the ally during the test because the material spends a relatively shrt time at the test temperature and the precipitatin strengthening has already ccurred at a lwer temperature during the heating stage f the test. Calculated phase fractin diagrams fr fur representative allys are shwn in Fig. 3. Intermctallic phases that were predicted t frm but are knwn t have slw kinetics, such as r\ in ally, 6 in ally, and \x in and allys, were suspended frm the calculatins in rder t represent the phase mixture that is likely t frm frm the slutinannealed allys during a shrt-term test. Bth Y and Y' are knwn t cexist in ally, but the experimentally measured rati f Y' t Y fractin is greater than what is predicted in Fig. 3 (Ref. 12). It was necessary t add the tw phase fractins tgether fr ally t cnfrm t the trend in Fig. 2. While Y' is thught t frm after a relatively lng time, it is clear that ally strengthened substantially during the time scale f the CHRT prcedure, as evidenced by the 77 t 83 ksi yield strength shwn in Table 2 fr the and T test temperatures. It is nt certain whether the WELDING JOURNAL

6 Fig. 8 Fracture surface f a ally CHRT specimen tested at the minimum ductility temperature. Light ptical images f the test specimen shwing intergranular cracking. A and B Brittle intergranular and ductile rupture regins n the fracture surface. Secndary electrn images; C intergranularfractureregin; D ductile regin. Fig. 9 Fracture surface f a ally CHRT specimen tested at the minimum ductility temperature. A and B Light ptical images f the test specimen shwing the fracture surface. Secndary electrn images; C Mixed ductile rupture; D intergranular mde f fracture. strengthening is caused by precipitatin f y, /', r bth in the CHRT prcedure. The CHRT gave elngatin values f 2 t 3% at F ( C), while three tensile tests f ally (heat ) in the fully aged cnditin [ F ( C) 8 h] gave 8, 11, and 18% elngatin at F. The ally exhibited significantly greater ductility in the aged cnditin than in the CHRT, even thugh the yield strength was slightly higher in the aged cnditin. Metallgraphy revealed that the ally develped grain bundary carbides after the standard-aging treatment, which were nt present after the CHRT. Grain bundary precipitates that frm during the standard aging treatment may strengthen the grain bundaries and increase resistance t intergranular cracking. These precipitates d nt have time t frm during the CHRT, even thugh the ally has sufficient time t develp mst f its strength, which may cntribute t the very lw ductility exhibited in the CHRT. A similar phenmenn may be expected t ccur during heat treatment f material fabricated in the slutin-annealed cnditin. Alternatively, the lw ductility displayed by ally in the CHRT has been attributed t precipitatin f hyperfine Y n heating, which may carsen during the standard aging treatment (Ref. 1). Cmparisn f CHRT t Other Tensile Test Methds The CHRT results are cmpared t results f ther tensile test methds fr a set f five allys with varying levels f "/'-frming elements in Fig. 4. The results in Fig. 4 are frm five different allys; the cntent f /-frming elements is nt the nly cmpsitinal variable. Each symbl represents a single test result. Tw r three replicates are pltted fr each cnditin s that the reprducibility f the test methds can be seen. All allys were tested at F ( C), which is very clse t the minimum ductility temperature fr each ally. It is expected that, in general, the susceptibility t strain-age cracking increases as the cntent f /-frming elements increases in the ally. Linear regressin lines are used in Fig. 4, nt t suggest a theretical basis fr a linear trend, but simply t illustrate that the CHRT data shw a decreasing trend in CHRT elngatin as a functin f increasing cntent f /-frming elements, while the ther tensile test methds d nt shw a cntinuus trend. The CHRT results gave a better crrelatin (R 2 = 0.80) with the ttal cntent f /-frming elements in the ally than the ther tw test methds (R 2 = 0.53 and 0.58), as indicated in Fig. 4. The result f hlding at the test temperature fr 20 min was t increase ductility fr sme allys and decrease ductility fr ther allys in cmparisn t the CHRT, in which the test was cnducted immediately upn reaching the test temperature. Hlding at the test temperature fr 5 min prduced variable results and was nt pursued further. There is n trend line fr the 5-min-attemperature test in Fig. 4 because f limited data. Cmparisn f CHRT results t 20- min-at-temperature results in Fig. 4 reveals that ductility decreases with hlding time fr sme allys while increasing r remaining cnstant fr thers. The effect f hlding times in the precipitatin temperature range was nt pursued further because hlding times are nt relevant t actual fabricatin practice. The results f the ASTM test were similar t the 20-min-at-temperature test, but with increased ductility as a result f the higher strain rate. Strain rate has been shwn t have a significant effect n the measured ductility f ally (Ref. 9). Sensitivity t strain rate is cnsistent with a mechanism f envirnmental embrittlement by xygen. The CHRT ffers the advantage f simulating the micrstructure that wuld ccur in a fabricatin during the initial heating cycle t the slutin-annealing temperature, while the ther tensile test methds, which invlve lnger hlding FEBRUARY 2006

7 Illillllllilllllll Fig. 10 Crss sectins f the fracture surfaces f CHRT test specimens tested near the minimum ductility temperature. Fig. 11 Micrstructures near the fracture surface f CHRT specimens tested near the minimum ductility temperature. times, d nt simulate the prcess f pstweld heat treatment. Furthermre, the relatively slw strain rate used in the CHRT mre clsely simulates the slw buildup f strain in a restrained fabricatin than wuld a faster strain rate. Cmparisn f CHRT Results t a Predictr f Strain-Age Cracking Resistance Thumberaj et al. (Ref. 13) investigated the influence f chemical cmpsitin n strain age cracking f Rene-41 ally. Using the heat cmpsitins and CHRT results reprted by Fawley ct al. (Ref. 1) and sme thers, they crrelated the CHRT results t chemical cmpsitin using regressin analysis. An empirical parameter called DUCT was develped, which predicted susceptibility f ally heats t strain-age cracking. Higher values f DUCT indicated greater ductility and greater resistance t cracking. The empirical relatinship indicated a beneficial influence f carbn and brn, and a detrimental influence f silicn n CHRT results. Values f DUCT were calculated fr each f the allys tested in the present prgram, and are given in Table 1. Fr each f the allys having data fr multiple heats, the CHRT elngatin is pltted as a functin f DUCT in Fig. 5A. The DUCT parameter successfully predicted the better-perfrming heats fr and allys, but nt fr ally. The valid crrelatin fr and allys suggests that carbn and brn have a beneficial influence and silicn has a detrimental influence n CHRT behavir in bth allys. Brn is knwn t imprve resistance t intergranular cracking and carbn may strengthen grain bundaries thrugh carbide precipitatin, r it may limit grain grwth by carbide pinning f grain bundaries. The DUCT parameter was develped by regressin analysis n heats f ally nly, s it fllws that it wuld predict the perfrmance f a similar ally such as, but nt effectively predict the perfrmance f a very different ally such as. Furthermre, DUCT des nt take int accunt the influence f variatins in Y-frming elements because these were held relatively cnstant in the heats f ally frm which DUCT was develped, whereas the minr elements, carbn, brn, and silicn, varied in these heats t a greater extent. Fawley et al. cmmented that high silicn prmtes grain grwth, but did nt explain the mechanism fr this phenmenn (Ref. 1). Fawley et al. pltted the minimum CHRT elngatin as a functin f the inverse square rt f grain diameter and fund a linear relatinship (Ref. I). The strng trend suggested that grain size is the main surce f heat-t-heat variatins in Rene 41 ally, and that cmpsitinal variatins are imprtant in sfar as they influence grain size. In the present investigatin, the best-perfrming heats f ally and ally had a slightly finer grain size than the ther heats, as indicated in Table 2. In Fig. 5B. the CHRT ductility is pltted against a functin f bth grain diameter and the DUCT chemical cmpsitin parameter, prducing a favrable crrelatin fr all three allys. While the present data set is t small t develp a reliable empirical relatinship, the results indicate that bth grain size and chemical cmpsitin are imprtant variables in determining strain-age cracking behavir. Fractgraphy and Metallgraphy Strain-age cracking failures typically exhibit an intergranular fracture surface (Refs. 1, 2). Fractgraphy was carried ut n the CHRT specimens t determine if the test simulated this intergranular cracking phenmenn. A set f fur allys, including,,, and, was selected t illustrate the range f fractgraphic behavir exhibited amng the allys tested. Details f the fracture surfaces are shwn in Figs The allys that exhibited relatively lw ductility, (Fig. 6), (Fig. 7), and (Fig. 8), exhibited regins f brittle, intergranular fracture that initiated frm the surface and prpagated int the center f the specimen. This was especially visible in the case f ally (Fig. 8). Smewhat different behavir was exhibited by ally in that intergranular fracture did nt appear t initiate frm the surface. Ally exhibited the greatest resistance t cracking f the allys tested. Fracture ccurred by a mixture f ductile rupture and intergranular separatin thrughut the thickness f the specimen. Crss sectins f the fractured specimens are shwn in Fig. 10. Intergranular cracks that initiated frm the surface are clearly visible in and allys. WELDING JOURNAL

8 iimmihimsmm " :. In the case f, the entire specimen thickness separated by brittle-intergranular fracture at the lcatin f the crss sectin shwn in Fig. 10, althugh there were als areas f ductile rupture, as shwn in Fig. 8. The fracture f ally was ductile with single grain facets that separated by intergranular cracking scattered thrughut the thickness. Micrstructures near the fracture surface are shwn in Fig. 11. Lcatins f intergranular cracking are shwn fr,, and ally. In the case f ally, the ductile fracture surface is shwn with a few internal intergranular separatins that did nt prpagate int cracks. The presence f intergranular cracking suggests that the phenmenn f strain-age cracking had successfully been reprduced in the CHRT. Strain-age cracking is knwn t prpagate intergranularly. The initiatin f cracking at the surface f the specimens suggests envirnmental embrittlement by xygen (Refs. 1, 4, 14). While embrittlement by xygen appears t cntribute t a further reductin in ductility, it was nted that heat treatment in vacuum imprves ductility but des nt entirely eliminate cracking in Rene 41 ally (Ref. 14). Summary Ranked accrding t the CHRT minimum elngatin, the susceptibility f wrught superallys t strain-age cracking is as fllws frm greatest t least:,, PK-33,,, and. Ally exhibited lw ductility ver a lesser temperature range than the ther allys, which is nt taken int accunt in ranking the allys simply by minimum ductility. The CHRT minimum ductility crrelated well with the sum f Al+Ti+Nb n an at- % basis and with the calculated fractin f i at 500 C. The CHRT prvided an effective and ecnmical means f ranking allys, and gave a ranking that was cnsistent with expectatins based n the literature. Acknwledgments Rupinder Sharma and Lee Pike f Haynes Internatinal are gratefully acknwledged. Sharma perated the cntrlled heating rate tensile test apparatus and Pike prvided technical input and assisted with Pandat calculatins. References 1. Fawley, R. W, Prager, M, Carltn, J. B., and Sines, G Recent studies f cracking during pstwclding heat treatment f nickel-base allys. WRC Bulletin N Welding Research Cuncil, NY. 2. Lepkwski. W. J., Mnre, R. E., and Ricppcl, P. J Studies n repair welding agehardenable nickel-based allys. Welding Jurnal 39(9):392-st400-s. 3. Weiss. S Hughes, W P., and Mackc, H. J Welding evaluatin f high temperature sheet materials by restrained patch testing. Welding Jurnal 41(1): 17-st22-s. 4. Thmpsn, E. G., Nunez, S., and Prager. M Practical slutins t strain-age cracking f Rene 41. Welding Jurnal 47(7): 299-s t 313-s. 5. Hughes, W. P., and Berry, T. F A study f the strain-age cracking characteristics f welded Rene 41 Phase I. Welding Jurnal 46(8): 361-s t 370-S. 6. Wu, K. C, and Herfert, R. E Micrstructural studies f Rene 41 simulated weld heat-affected znes. Welding Jurnal 46(1): 32-s t 38-s. 7. Dix, A. W, and Savage, W. F Factrs influencing strain-age cracking in Incnel. Welding Jurnal 50(6): 247-s t 252-s. 8. Franklin, J. E., and Savage, W F Stress relaxatin and strain-age cracking in Rene- 41 weldments. Welding Jurnal 53(9): 380-s t 387-s. 9. Naka, Y Study n reheat cracking f Ni-based superally. Waspally. Transactins f the Japan Welding Sciety, 19(1): Lin, W A methdlgy fr quantifying pstweld heat treatment cracking susceptibility. Abstracts f papers, 81st Annual AWS Cnventin, p Nrtn, S.. and Lippld, J. C Develpment f a Gleeble-based test fr pstweld heat treatment cracking susceptibility. Abstracts f papers, 82nd Annual AWS Cnventin, p Chaturvedi. M. C. and Han, Y Strengthening mechanisms in Incnel superally. Metal Science 17(3): Thamburaj, R., Gldak, J. A., and Wallace, W The influence f chemical cmpsitin n pst-weld heat treatment cracking in Rene-41. SAMPE Quarterly, (7): p D 1 Anessa, A. T, and Owens. J. S Effects f furnace atmsphere n heat treat cracking f Rene 41 weldments. Welding Jurnal 52(12): 568-s t 575-s. Papers are Sught fr American Welding Sciety's 2006 Prfessinal Prgram MIAMI - December 22, The American Welding Sciety's Technical Papers Cmmittee has issued a call fr papers fr the Prfessinal Prgram at the 2006 FABTECH Internatinal & AWS Welding Shw, scheduled fr Octber 31-Nvember 2 at the Gergia Wrld Cngress Center in Atlanta, Gergia. The Prfessinal Prgram will include presentatins n tpics f interest t welding practitiners and managers, researchers, and advanced students. Papers are sught in three categries: Technical/Research Oriented, invlving new science r engineering relevant t welding, jining, and allied prcesses. Applied Technlgy, invlving new r unique applicatins f knwn principles f jining science r engineering. Welding Educatin, invlving successful educatin and training methds at all levels that are relevant t the welding industry. Papers may be prcess-riented r materials-riented, and may include mdeling f welding prcesses. Preference will be given t papers with a clearly cmmunicated benefit t the welding industry. Abstracts may be submitted using the frm enclsed in this issue f the Welding Jurnal at the end f the Research Supplement r the nline frm lcated at Fr mre infrmatin, cntact Gladys Santana, AWS manager f cnferences and seminars, at (800/305) , ext. 223, r via at gladys@aws.rg. FEBRUARY 2006