Cast Ni-base Superalloy Research Articles

Serrated grain boundary formation potential of Ni-based superalloys and its implications

The serrated grain boundary formation potential of a large number of conventionally forged, powder processed, and investment cast Ni-based superalloys is reviewed. A mechanism of serrated grain boundary formation by which grain boundaryγ′ particles move and displace the local grain boundary segment is discussed and the prerequisite conditions for its occurrence are highlighted. The practical implications of the serrated grain boundary formation are also discussed. It is suggested that modifying the existing heat-treatment cycles in some investment cast and powder processed Ni-based superalloys would improve their properties. The possibility of minimizing weld cracking in superalloys by creating serrated grain boundaries in the base metal and the heat affected zone is also discussed.

STUDY ON RELATIONSHIP OF PHASES IN ALLOYS BY MEANS OF EPMA

Phase diagram is of both academic and technological interest. A pseudo-ternary phase diagram of Ni-(Al + Ti ) - (Cr + Mo) of Ni-base superalloy was constructed as well as Fe-Mn-Al ternary phase diagram by means of EPMA. The effect of boron on porosity of cast Ni-base superalloys was revealed through studying the solidification process. It was shown that EPMA is a very useful method for the studying relationship of phases in alloys.

The effects of Cr, Al, Ti, Mo, W, Ta, and Cb on the cyclic oxidation behavior of cast Ni-base superalloys at 1100 and 1150�C

A series of cast nickel-base y/y′ superalloys as systematically varied at two nonzero levels of Cr, Al, Ti, Mo, Cb, W, and Ta with nominally fixed levels of 10 at. % Co, 0.06 at. % C, 0.05 at. % Zr, and 0.05% B. A 1/4-replicate 27-factorial statistical design supplemented by 18 additional alloys was used to estimate main effects and all two-factor interactions. The cyclic oxidation resistance was determined from specific weight change data as a function time for 1-hr cycles in static air at 1100 and 1150°C. A derived oxidation attack parameter, Ka, was fitted by multiple linear regression over the alloy sample space at each temperature. At the levels tested, Al was the most important alloy addition. The lowest Ka was achieved at the highest (13 at. %) test level of Al and the lowest (10 and 2 at. %, respectively) test levels of Cr and Ti. The results for the refractory metal additions were somewhat ambiguous, but the most oxidation-resistant composition was estimated to be 3 at. % Mo-1 at. % Cb-3 at. % W-3 at. % Ta for the compositions tested. X-ray diffraction analysis of the alloy scales indicated that at the lowest Ka value, most oxidation resistant alloys were associated with alumina-aluminate spinel formation at the high Al levels. Higher boron contents, which were unintentionally varied, were clearly detrimental even for the most resistant compositions. High boron contents apparently trigger nonprotective NiO formation. In addition, tri-rutile type oxides were found on all test alloys, but these were not considered to be harmful to oxidation resistance.

An evaluation study of aluminide and chromoaluminide coatings on IN-100

Aluminide diffusion coatings are commonly used to protect aircraft gas turbine blades and vanes from oxidation and hot-corrosion attack. These coatings are based on NiAl intermetallic compound with other alloying elements like Cr and Ti either diffused from the superalloy substrate or incorporated in a separate coating step. The present investigation is mainly concerned with the development of both aluminide and chromoaluminide coatings on IN-100, a cast Ni-base superalloy. The coating structure and composition have been characterized and the cyclic oxidation and hot corrosion properties have been evaluated for the different types of coatings. The difference in the hot-corrosion properties between the aluminide and the chromoaluminide coatings has been rationalized in terms of the coating chemistry. The mode of coating degradation under hot-corrosion conditions has also been analyzed.

Ni基耐熱合金の溶接性に関する研究(第8報)

Up to this time, the authors studied the weld cracking phenomena in typical and fundamental cast Ni-base superalloy, Inconel 713C, to get information on the weld cracking phenomena of cast Ni-base superalloys.It is the purpose of this study to clarify the main cause of weld cracks in cast Ni-base superalloy, B-1900 which has more excellent mechanical properties than those of Inconel 713C, according to the information about hot cracking phenomena in Inconel 713C.From experimental results, it was made clear that weld cracks in B-1900 were hot cracks and the main cause of hot cracks was low melting point-fine white constituents crystallized at grain boundaries.