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Microstructural analysis of weld cra...

Vishwakarma, Krutika.

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Microstructural analysis of weld cracking in 718 Plus superalloy.

紀錄類型:	書目-語言資料,印刷品 : Monograph/item
正題名/作者:	Microstructural analysis of weld cracking in 718 Plus superalloy./
作者:	Vishwakarma, Krutika.
面頁冊數:	268 p.
附註:	Source: Dissertation Abstracts International, Volume: 69-01, Section: B, page: 0644.
Contained By:	Dissertation Abstracts International69-01B.
標題:	Engineering, Materials Science. -
電子資源:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=NR36278
ISBN:	9780494362785

Microstructural analysis of weld cracking in 718 Plus superalloy.
Vishwakarma, Krutika.

Microstructural analysis of weld cracking in 718 Plus superalloy. - 268 p.

Source: Dissertation Abstracts International, Volume: 69-01, Section: B, page: 0644.

Thesis (Ph.D.)--University of Manitoba (Canada), 2008.

Allvac 718RTM PLUS(TM) (718 Plus) is a new Ni-base superalloy developed to be used in land and aero gas turbine applications. 718 Plus was developed to have high temperature properties superior to its baseline superalloy Inconel 718, while maintaining its workability. Besides its high temperature properties superior to Inconel 718, limited information exists about its physical metallurgy or weldability. This project studied the microstructure and electron beam welding response of this new superalloy in two selected pre-weld heat treated conditions. To further understand the effect of minor alloying elements on its weldability, two versions of 718 Plus with varying concentrations of boron and phosphorus, HC 49 with higher B and P and HC 20 with normal B and P, were also studied. Finally, the weldability of 718 Plus alloys was compared to that of Inconel 718 and Waspaloy under similar welding conditions.

ISBN: 9780494362785Subjects--Topical Terms:

1017759
Engineering, Materials Science.

Microstructural analysis of weld cracking in 718 Plus superalloy.
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245 1 0 $a Microstructural analysis of weld cracking in 718 Plus superalloy.
300 $a 268 p.
500 $a Source: Dissertation Abstracts International, Volume: 69-01, Section: B, page: 0644.
502 $a Thesis (Ph.D.)--University of Manitoba (Canada), 2008.
520 $a Allvac 718RTM PLUS(TM) (718 Plus) is a new Ni-base superalloy developed to be used in land and aero gas turbine applications. 718 Plus was developed to have high temperature properties superior to its baseline superalloy Inconel 718, while maintaining its workability. Besides its high temperature properties superior to Inconel 718, limited information exists about its physical metallurgy or weldability. This project studied the microstructure and electron beam welding response of this new superalloy in two selected pre-weld heat treated conditions. To further understand the effect of minor alloying elements on its weldability, two versions of 718 Plus with varying concentrations of boron and phosphorus, HC 49 with higher B and P and HC 20 with normal B and P, were also studied. Finally, the weldability of 718 Plus alloys was compared to that of Inconel 718 and Waspaloy under similar welding conditions.
520 $a Hot rolled wrought plates of Inconel 718, Waspaloy and 718 Plus alloys were supplied by ALLVAC Inc. 12.7 mm x 12.7 mm x 101.6 mm sections were cut normal to the rolling direction of the plates and were subjected to their recommended respective solution heat treatments, viz., 950°C for 1 hour for 718 Plus alloys and Inconel 718 and 1020°C for 1 hour for Waspaloy. 718 Plus alloys and Inconel 718 were also examined after another solution heat treatment at 1050°C for 1 hour. All the heat treatments were followed by water quenching. Thorough microstructural characterization before and after welding was carried out using optical microscopy, analytical scanning electron microscopy, electron microprobe analysis and analytical transmission electron microscopy. In addition, Secondary Ion Mass Spectrometer (SIMS) was used to study the grain boundary segregation in the two 718 Plus alloys.
520 $a Interestingly, the microstructure of 718 Plus alloy, in the heat treated conditions it was studied, was very similar to that of Inconel 718 despite of the considerable difference in their chemistries. The main discernible difference was the formation of gamma' as the main strengthening precipitate in 718 Plus alloys in the as received and 950°C solution heat treated condition. The other phases present in the pre-weld microstructure were Nb rich MC type carbides, Ti rich carbonitrides and grain boundary delta phase.
520 $a Solution heat treated plates of all the three alloys were welded with a sharp focus electron beam with the welding parameters of 44 kV voltage, 79 mA current and 152 cm/min speed. The microsegregation pattern of 718 Plus during solidification of the fusion zone indicated that while Fe, Co, W and Cr segregated to the core of the gamma dendrites, Nb, Ti and Al were extensively rejected into the interdendritic liquid. Electron diffraction and x-ray microanalysis using transmission electron microscopy (TEM) of the fusion zone showed that the major secondary phases that formed from the interdendritic liquid were gamma/MC type carbide eutectic and gamma/Laves eutectic constituents.
520 $a Heat affected Zone (HAZ) microfissuring due to liquation was observed in all the alloys with resolidified products on the liquated and resolidified grain boundaries. Grain boundary liquation and segregation of minor alloying elements was considered to he the primary reason for liquation of HAZ grain boundaries which caused cracking. Evidence of constitutional liquation of Nb rich MC type carbides in 718 Plus was found in the region adjacent to the fusion zone and also on the cracked grain boundaries. The resolidified products along the microfissures consisted of gamma + Laves and gamma + MC type carbide eutectics. Complete and partial healing of microfissuring by backfilling was also observed.
520 $a Segregation of B was detected by SIMS on the grain boundaries of both the 718 Plus alloys, with higher concentration of Bon HC 49 grain boundaries. Also, for the first time, P was detected by SIMS on the cracked grain boundaries on both the alloys, which confirmed that grain boundary segregation of B and P was directly related to microfissuring.
520 $a Weldability evaluated by using weld cracking measurement and hot ductility measurements, using Gleeble Thermo-mechanical simulator, suggested that weldability of the lower B and P alloy was comparable to that of Inconel 718. An increase in B and P in 718 Plus alloy however, deteriorated the weld cracking resistance and the on-cooling hot ductility values. Cracking in all the alloys increased with an increase in the solution heat treatment temperature. Cracking in Waspaloy was significantly more pronounced than that observed in the other alloys. The hot ductility and welding measurements were in agreement with each other and indicated that the cracking susceptibility of the alloys increased in the following order--Inconel 718 < lower B and P 718 Plus alloy < higher B and P 718 Plus alloy.
590 $a School code: 0303.
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