本研究Inconel 718超合金以TIG與PAW對接銲，在不同熱處理條件下施以拉伸試驗及微硬度試驗，比較銲接機械性質的差異；另外使用可調應變試驗以評估Inconel 718超合金銲接熱裂縫敏感性。金相與SEM觀察則用以研究上述試驗產生的微觀組織及裂縫。
拉伸試驗結果顯示，有填料銲件之機械性質明顯高於無填料的銲件，而三種不同熱處理條件皆有助於提高機械性質。TIG銲件機械性質比PAW銲件之機械性質為佳，但以相同熱處理條件後，兩者機械性質趨於一致。
可調應變試驗的結果顯示，相同外加應變量下，裂縫總長度會隨熱循環次數增加而增加，而在相同熱循環次數下，裂縫總長度均隨著外加應變量之增加而增加，故熱循環次數與外加應變量增加會提高熱裂敏感性。
金相顯微觀察，熔融區皆為樹枝狀組織。經三種熱處理後，CHT及1950H熱處理之熔融區為柱狀樹枝狀組織，而MHT熱處理熔融區為等軸晶組織。熱裂縫主要出現在銲道與熱影響區交界之部分熔融區，屬於沿晶裂縫，熔融區裂縫較粗
大，熱影響區微小且少。從破斷面分析，熱裂縫之銲道熔融區屬於凝固熱裂，在熱影響區屬於液化熱裂；銲接拉伸破斷面皆屬延性破壞。

There are two purposes of this research: one is to compare the mechanical properties of the Inconel 718 Weldments using two different welding processes, Gas Tungsten Arc Welding(GTAW) and Plasma Arc Welding(PAW). The weldments were then undergone tensile test and microhardness test after different heat treatments. The other purpose is to evaluate the hot cracking susceptibility of the welded Inconel 718 using the Varestraint test. Metallographic and SEM observation were used to study the microstructure and cracking mechanism resulted from the above experiments.
From the results of tensile tests, the mechanical properties of weld metal with filler metal is higher than that without filler metal. The mechanical properties of all the weldment with different heat treatments are better than those of the weldment without heat treatments. Among all of the GTAW and PAW weldments, the mechanical properties of GTAW weldment are better, but after heat treatments, the mechanical properties of both become the same.
From the results of the Varestraint test, with the same augmented strain, the total crack length of the specimens increases with the increase of the number of thermal cycling. With the same number of thermal cycling, the total crack length increases with the increase of augmented strain. Therefore, the increase of multiple thermal cycling and augmented strain can raise the weld hot cracking susceptibility.
From the metallographic microstructure observation, the fusion zone are all columnar dendritic. However, after three different hot treatments, the fusion zone becomes equiaxed after MHT treatment, while the fusion zone remains in columnar dendritic type after CHT or 1950H hot treatment. Hot cracks are intergranular type, mainly appear in partially melted zone which is between the fusion zone and the heat affected zone. The crack in fusion zone is much thicker and bigger while that in the heat affected zone is few and tiny. Besides, the fracture surface of cracking have displayed solidification cracking in the fusion zone and liquation cracking in the heat affected zone. The ductile fracture surface was observed in all tensile tested specimens.

AWS. (1978). Welding Handbook. Vol.2.7ed.
Barker, J.F. & Ross, E.W. (1970). Long Time Stability of Inconel 718.Journal of Metals,
(1), pp.31-41.
Barker, J.D. (1962). A Superalloy for Medium Temperature. Metal Process: 5, pp.72-75.
Bochvar, A.A. & Sidevskaya, Z.A. (1947). Failure of Castings Caused by Shrinkage Stresses During Crystallization,as Related to Cosition. Izvest Akad.,NAVK SSSR.
Boesch, W.J. & Canada, H.B. (1969). Precipitation Reactions and Stability of NI3Cb in Inconel 718. Journal of Metals, (10), pp.34-39.
Bolgna, D.J. (1969). Metallurgical Factors Influencing the Microfissuring of Alloy 718 Weldments. Metal Engineering Quarterly, p.37.
Borland, J.C. & Younger, R.N. (1960). Some Aspects of Cracking in Welded Cr-Ni Austenitic Steels. British Welding J.7(1), pp.22-59.
Borland, J.C. (1960). Generalized Theory of Super-Solidus Cracking in Welds(and Casting). British Welding J.7(8), pp.508-512.
Bulletin of Humtington alloys(1978).Inconel Alloy 718(3ed).
Burer, J.A. & Hanind, D.K. (1967). Heat Treating Nickel-Base Superalloy. Metal Prog
ress, (7), pp.61-67.
Cary, H.B. (1988). Modern Welding Technology(3rd ed). Englewood Cliff, New Jersey,
Prentice-Hall Inc.
Chaturvedi, M.C. & Chung, D.W. (1981). Yielding Benavior of a γ" Precipitation Strengthened Co Ni Cr Nb Fe Alloy. Met.Trans: Vol. 12A, pp.77-81.
Chaturvedi, M.C. & Chung, D.W. (1979). Effect of Iron addition on the Precipitation
Behavior of Co Ni Cr Alloy Containing Nb. Met Trans: Vol. 11, p.1579.
Collins, H.E. (1969). Relative Long-Time Stability of Carbide and Intermetallic Phase in
Nickel-Base Superalloys. Trans of ASM: Vol.62, p.82.
Cooper, J.G. & Browning, J.A. (1965). Recent Developments in Plasma Welding. Journal
of Welding, p.268.
Cozar, R. & Pineal. (1973). Morphology of γ"and γ´ Precipitates and Thermal Stability of
Inconel 718 Type Alloys. Met.Trans: Vol. 4, p.47.
Dcker, R.F. (1979). Strengthening Mechanisms in Nickel-Base Superalloys. Source Book
on Materials for Elevated Temperature Applications ASM, pp.147-170.
Dix, W.A. & Savage, W.F. (1971). Factors Influencing Strain-Age Cracking in Inconel X-750. Journal of Welding, 50(6), pp.247-s.
Dolby, R.E. & Saunders, G.G. (1977). Underclad Cracking in Nuclear Vessel Steel. Metal
Construction, 1-9(9), pp.562-566.
Duall, D.S. & Owczarski, W.A. (1969). Studies of Postweld Heat-Treatment Cracking in Nickel-Base Alloy. Journal of Welding, 48(1), p.10.
Easterling, K.E. (1992). Introduction to the Physical Metallurgy of Welding. Oxford;
Boston: Butterworth Heinemann(2nd), p.205.
Filipski, S.P. (1964). Plasma Arc Welding. Journal of Welding, pp937.
Gordine, J. (1971). Some Problems in Welding Inconel 718. Welding Research Supple-
ments, pp.480-s.
Hall, R.C. (1967). The Metallurgy of Alloy 718. Journal of Basic Engineering Trans ASM, pp.511-516.
Hemsworth, B., Bohiszewski, T. & Eaton, N.F. (1969). Classification and Definition of High Temperature Welding Cracks in Alloys. Metal Construction & Brit.W.J.,1(2),
pp5-16.
James, L.A. (1978). Fatigue-Crack Growth in Inconel 718 Weldments at Elevated Temperature. Journal of Welding, 57(1), pp.17-s.
Kammer, P.A., Masubuchi, K. & Monoe, R.E. (1964). Cracking in High-Strength Steel Weldments—A Critical Review. DMIC Report 197.
Kaufman, M. & Palty, A.E. (1961). The Phase Structure of Inconel 718 and 702 Alloy.
Trans of AIME,221(12), pp.1253.
Kirman, I. & Warrington, D.H. (1970). The Precipitation of Ni3Nb Phases in a Ni-Fe-Cr-
Nb Alloy. Met.Trans: Vol. 1,10, pp.2667-2675.
Kim, W.H. & Na, S.J. (1998). Heat and Fluid Flow in Pulsed Currrent GTA Weld Pool.
International Journal of Heat and Mass Transfer,Vol.11, pp.3213-3227.
Kotval, P.S. (1969). Idendification of the Strengthening Phase in Inconel 718. Trans of AIME,242(8), p.764.
Kume, R., Okabayashi, H. & Amano, M. (1947). Susceptibility to Underclad Cracking-
combined Effects of Residual Strain and Heat-Affected Zone Ductility. Journal of
Engineering Materials and Technology, 98(10), pp.348-356.
Matsuda, F. (1990). Hot Crack Susceptibility of Metal",Advances in Welding Metallurgy.
JWS, pp.26-58.
Mayer, R.A. (1972). Selected Mechanical Properties of Inconel 718 and 706 Weldments. Journal of Welding, 55(9), pp.269-275.
Mckeown, D. (1970). Versatile Weld Metal Cracking Tests. Metal Construction, 2(8),
pp.351-352.
Mckeown, D. (1971). Re-Heat Cracking in High Nickel Alloy Heat-Affected Zone. Journal of Welding, 50(5), p.201.
Mclean, W. & Pinfor, B.E. (1974). Operational Envelops for Plasma Keyhole Welding
Process. 3rd International Conference,Vol.1, p.93.
Metcalfe, J.C. & Quigley, M.B.C. (1975). Keyhole Stability in Plasma Arc Welding.
Welding Research Supplement, pp.401-s.
Moll, J.H., Maniar, G.N. & Muzyka, D.R. (1971). The Microstructure of 706,a New
Fe-Ni-Base Superalloy. Met Trans: Vol. 2,8, pp.2143-2151.
Moll, J.H., Maniar, G.H. & Muzyka, D.R. (1971). Heat –Temperature of 706 Alloy for
Optimum 1200 oC Stress-Rupture Properties. Met Trans: Vol.2,8, p.2153.
Muller, J.F. & Donachie, M.J. (1975). The Effect of Solution and Intermediate Heat Trea-
tments on the Notch-Rupture Behavior of Inconel 718. Met Trans: Vol.6A,13,
p.2221.
Muzyka, D.R. (1971). Controlling Microstructures and Properties of Superalloys Via Use of Precipitated Phase. Metal Engineering Quaterly, (11), p.12.
Muzyka, D.R. &.Maniar, G.N. (1969). Effects of Solution Treating Temperature and Microstructure on the Properties of Hot Rolled 718 Alloy. Metal Engineering Quarterly,Nov, p.261.
Oblak, J.M. & Daulonis, D.F. (1974). Coherency Strengthening in the Ni Base Alloy Hardened by Do22 γ" Precipitates. Met.Trans: Vol. 5, pp.143-153.
Paulonis, D.F., Oblak, J.M. & Duuall, D.S.(1969). Precipitation in Nickel-Base Alloy 718. Trans of the ASM: Vol. 62, p.611.
Pender, J.A. (1986). Welding.( 3rd ed), New York: McGRAW-Hill Ryerson Ltd,pp.180-
191.
Qutist, W.E. & Taggart, R. (1971). The Influence of Iron and Aluminum on the Precipti-
tation of Metastable Ni3Nb Phases in the Ni-Nb System. Met.Trans: Vol. 2,3, pp.
825-831.
Raghavan, M. (1977). Precipitation in a Cu-30pct Ni-1pct Nb Alloy. Met Trans: Vol 8A,
p.1071.
Rizzo, F.J., & Buzzanell, J.D. (1969). Effect of Chemistry Variations on Structural
Stabilbty of Alloy 718. Journal.of Metals, (10), pp.24-34.
Savage, W.F. & Lundin, C.D. (1965). Welding Research Supplement. Journal of Welding, 44(10), pp.433-442.
Savage, W.F. & Lundin, C.D. (1965). The Varestraint Test. Journal of Welding, 44(10),
pp.433-442.
Sullivan, C.P.,& Donachie, M.J.(1971). Microstructures and Mechanical Properties of
Iron-base(-Containing)Superalloys. Metal Enginerring Quarterly, ( 11), pp.1-11.
Sullivan, C.P. & Donachi, M.J. (1979). Some effects of Microstructure on the mechanical Properties of Nickel-Base Superalloys. Source Book on Materials for Elevated-
Temperature Applications ASM, pp.250-259.
Sims, C.T. & Hagel, W.C. (1972). The Superalloys.
Sims, C.T.(1966). A Comtemportary View of Nickel-Base Superalloys. Journal of Metals
Oct, pp.1119-1130.
Thamburaj, R., Wallace, W. &Goldale, J.A. (1983). Postweld Heat-Treatment Cracking in
Superalloys. Inernational Metals Reviews, (28), p.1.
Thompson, E.G. (1969). Hot Cracking Studies of Alloy718 Weld Heat Affected Zone.
Journal of Welding, 48(2), pp.70-s.
Thompson, R.G. & Gengulu, S. (1983). Microstructural Evolution in the HAZ of Inconel 718 and Correlation with the Hot Ductility Test. Journal of Welding, 62(12), p.337.
Thompson, R.G., Cassimus, J.J., Mayo, D.E. & Dobbs, J.R. (1985). The Relationship
Between Grain Size and Microfissuring in Alloy 718. Journal of Welding, 51(3),
pp.91-s.
Tomsic, M.J. & Jackson, C.E. (1974). Energy Distribution in Keyhole Mode Plasma Arc Welds. Welding Research Supplement, pp.109-s.
Turner, P.W. & Lundin, C.D. (1970). Effect of Iron on the Hot Cracking of Uranium Weld Metal-Part 1. Journal of Welding, 49(12), pp.579-587.
Yoshimura, H. & Winterton, K. (1972). Solidification Mode of Weld Metal in Inconel 718. Journal of Welding, 51(3), pp.132-s.
王維城(民74)。Inconel 718電漿銲接與熱處理特性之研究。國立台灣大學碩士論文。
林義成、吳佩學(民88)。電將銲槍熱傳分析研究。高雄：金屬工業中心。
晁成虎(民76)。多重熱循環對超合金718銲接性之影響。國立交通大學機械工程研究所碩士論文。
楊俊彬(民74)。Inconel 718惰性鎢極電弧銲接與熱處理特性研究。國立台灣大學
碩士論文。
蔡履文(民75)。410 不銹鋼銲接及銲補研究。國立台灣大學材料科學工程研究所。