Ni-Cr-Al alloys

Engstrom et al. (1997) looked at diffusion couples in Ni-Cr-Al alloys and found that extremely complex diffusion paths were possible, see for example (Figs. 11.23(a) and (b)). These seem strange, but they are all consistent with the observed... 

The presence of water vapour adversely affects the selective oxidation of elements such as aluminium and chromium from iron-base and nickel-base ° alloys. This is illustrated in Figure 7.2 for a Ni-Cr-Al alloy. Exposure in dry air results in a continuous external alumina film while exposure in moist air results in profuse internal oxidation of the Al. It has also been found that water vapour affects the selective oxidation of aluminium from TiA1.2i... 

Figure 8.17 Weight-change versus time data showing that increased chromium concenttation in Ni-Cr-Al alloys ( , Ni-8 wt% Cr-6 wt% Al A, Ni-15 wt% Cr-6 wt% Al) extends the initiation stage for hot corrosion attack induced by immersion in a crucible with 1 g Na2S04 in static air isothermally at 1000 °C.

Metallic-film on glass ND-filters have the flattest spectral response, over a wide range, of all classes of attenuation filters. They are composed of a vacuum-deposited metal film (mostly inconel , an Ni-Cr-Al alloy) on a glass substrate note that fused silica needs to be used to be suitable at near-UV wavelengths. Its attenuation action is by both reflection and absorption, and the reflected beam intensity needs to be considered carefully in any application in which reflected light is undesirable. 

In pure S2 vapour, at a pressure of 0.1 atm, Vineberg and Douglass (1986) demonstrated markedly reduced rates of sulphidation at 700 C (fig. 12) when 1 wt.% Y was added to a Ni-Cr-Al alloy. However, in mixed S2-O2 atmospheres at 500 to 700 C, Kung and Srinivasan (1990) failed to record any beneficial rare-earth effect when lwt.% Y was added to a model Fe-25Cr-6Al alloy. 

For Fe-Ni-Cr-Al alloys (310SS) of normal grain size, a scale composed of both alumina (internal) and chromia (external) was formed during oxidation when their Al content was around 5wt%. When the coatings have a nanocrystalline... 

Error caused by the strain of the sensor is included in the pressure measured by a thin-film sensor, demonstrated by the third term of equation [1]. In order to evaluate this error, a Ni-Cr-Al alloy (3) shown in Figure 4 was used. The temperature sensitivity of this alloy (3) is (-4-0) x 10 [(Q/Q)/ C], while its pressure sensitivity is 1x10 [(Q/ 2)/MPa]. These values are significantly smaller... 

Fe-Cr-Al and Ni-Cr-Al alloys are mainly used at temperatures over 1000°C, the chromia scale is no longer able to give any beneficial effect, due to volatilisation problems [20]. Reports have indicated, however, that nanocrystal stmcture can promote the diffusion of A1 in Ni-Cr-Al alloy coatings. The minimum aluminium content for formation of a-Al203 on a Ni-20Cr-Al alloy coating can be reduced to 2 wt% when the grain size is of the order of 60 nm [21]. 

Liu Z Y, Gao W, Dahm K and Wang F H (1997), The Effect of Coating Grain Size on the Selective Oxidation Behaviour of Ni-Cr-Al Alloy, Scripta Mater, 37, 1551-1558. 

Liu Z, Gao W, Dahm K L, Wang F, The effect of coating grain size on the selective oxidation hehaviour of Ni-Cr-Al alloy , Scripta Mater, 37 (1997) 1551-1558 Strauss D, Muller G, Schumacher G, Engelko V, Stamm W, Clemens D, Quadakkers W J, Oxide scale growth on MCrAlY bond coatings after pulsed electron beam treatment and deposition of EBPVD-TBC , Surf Coat Technol, 2001, 135(2—3), 196-201... 

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