Cast superalloys

The nature of this ereep depends on the material, stress, temperature, and environment. Limited ereep (less than 1%) is desired for turbine blade applieation. Cast superalloys fail with only a minimum elongation. These alloys fail in brittle fraeture—even at elevated operating temperatures. 

Lane, M.J. "Investment Cast Superalloys Challenge Wrought Material." Advanced Materials [Pg.303]

Molloy, VV J.. hisesiineni-Cast Superalloys a Cutod tnsestmenl. Adetau etl,Materials dt Professes, 21 1 October SJ90>,... 

EFFECT OF PROCESSING CONDITIONS ON STRUCTURE, PROPERTIES AND PERFORMANCE OF A NICKEL BASE CAST SUPERALLOY FOR HIGH TEMPERATURE APPLICATIONS... 

The present paper highlights the structure property relations in a Ni- base cast superalloy, which was processed in equiaxed and directionally solidified castings, through investment casting route. 

Effect of Processing Conditions on Structure, Properties and Performance of a Nickel Base Cast Superalloy for High Temperature Applications..357... 

Table 3.1-96 Nominal compositions of Ni-based cast superalloys...

In addition to the cast superalloys, there is the H series of cast Fe-Cr-Ni steels. A second letter is used in the designation of these steels to indicate loosely the nickel and, to a lesser extent, chromium content. In general, the higher the letter, the greater the nickel content. For example, the HK and HP alloys have nominally 20Ni-25Cr and... 

The selection of a cast superalloy. In this study, a series of cast Ni-base Vy superalloys were systematically varied at selected levels of Co, Cr, Mo, Ta, and Al, and the alloys weight change performance was monitored. A full factorial central experimental design was used, with five sets of star points to completely map the response of these alloys. For five elemental variables, 43 alloy compositions were required, and regression analysis of the results permitted the production of a complete second-degree equation describing the total variability of the alloy performance. 

Microfissuring. Similar to austenitic stainless steel, nickel alloys are susceptible to formation of liquation cracks in reheated weld metal regions or parent metal HAZ. This type of cracking is controlled by factors outside the control of the welder such as grain size or content impurity. Some alloys are more sensitive than others. For example, the extensively studied Inconel 718 is now less sensitive than some cast superalloys, which cannot be welded without inducing liquation cracks. 

Table 5. Chemical Composition of Cast Nickel-Base Superalloys, wt % ...

Using rapid solidification technology molten metal is quench cast at a cooling rate up to 10 °C/s as a continuous ribbon. This ribbon is subsequently pulverized to an amorphous powder. RST powders include aluminum alloys, nickel-based superalloys, and nanoscale powders. RST conditions can also exist in powder atomization. 

Detailed consideration of the structure of many of the advanced and complex alloys which are of considerable technological importance (high-strength titanium alloys, nickel-base superalloys, etc.) is beyond the scope of this section, other than to point out that no new principles are involved. Certain titanium alloys, for example, exhibit a martensitic transformation, while many nickel-base superalloys are age hardening. Similarly, cast irons, although by no means advanced materials, are relatively complex they are considered in Section 1.3 where graphitisation is discussed. 

These ceramics are usually coated by CVD with an appreciable increase in performance as shown in Fig. 18.1. A major use of these coated ceramics is in the machining of hard materials such as cast iron and superalloys.1 1... 

Solution databases now exist for a niunber of the major metallic alloy systems such as steels, Ni- based superalloys and other alloy systems, and highly accurate calculation have been made which even a few years ago would have been considered impossible. The number of substance databases are increasing and the numbers of substances they include is reaching well into the thousands. Substance and solution databases are increasingly being combined to predict complex reactions such as in gas evolution in cast-irons and for oxidation reactions, and it is already possible to consider calculations of extreme complexity such as the reactions which may occur in the burning of coal in a industrial power generator or the distribution of elements in meteorites. 

The distribution of nickel consumption by use in 1988 was as follows stainless and heat-resistant steel, 40% nonferrous alloys, excluding superalloys, 21% electroplating, 17% superalloys, 12% and other, 10%. Other uses include cast iron chemicals and chemical use electric, magnet, expansion alloys steel alloys, other than stainless steel batteries and ceramics. Eighty percent of nickel consumption was for the production of nickel metal and alloys (Kirk 1988a). 

---