QQ-N-286 Nickel-Copper-Aluminum Alloy, Wrought Uns N05500This specification covers all nickel-copper-aluminum alloy wrought forms formerly classified as class A. This alloy is designated under the Unified Numbering System for Metals and Alloys as UNS N05500. Except for cases where nonmagnetic properties are paramount, this alloy is intended to be age hardened prior to placing the material in service.

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QQ-N-286G micrometers is determined. The grain size shall be taken parallel to the fracture surface and as close to the fracture surface as practical.

4.3.6.4 Fracture surface analysis. After fracture, the fracture surface of each specimen shall be examined and the fracture mode characterized as follows:

4.3.6.4.1 Fracture surface photography. A series of eight (8)

photographs shall be taken of the fracture surface at equally spaced intervals

of 45 degrees around the specimen circumference, with the first site selected

randomly. Each photograph shall be taken using a scanning electron microscope

(SEM) at a magnification scaled to the grain size using the relationship

below:

M = 10,000/G

Where M is the magnification and G is the grain size in micrometers, m. If the calculated magnification is not a preset level on the SEM being used, the magnification shall be decreased to the nearest preset level. For grain

sizes larger than 15 m, a small portion of the machined notch root must be visible in each photograph. For grain sizes smaller than 15 m, the center of each photograph must be approximately 150 m from the notch root.

4.3.6.4.2 Determination of intergranular fracture sites. The photographs of 4.3.6.4.1 shall be used to determine intergranular fracture features. An intergranular fracture feature shall be defined as two adjacent and contiguous facets demarcated by a distinct grain boundary or three adjacent and

contiguous facets demarcated by grain boundaries that come together at a triple point. The facets shall be clearly identifiable as a grain surface, otherwise they shall not be considered in defining a site of intergranular fracture.

4.3.6.4.3 Quantification of intergranular fracture sites. The template illustrated in Figure 4 shall be transferred to a transparency that shall be

placed over each of the nominal 3� x 4� inch photographs obtained in

4.3.6.4.1 above. Intercepts with intergranular fracture features with the

circles on the template shall be counted for each photograph. An intercept

shall be defined as the intersection of one intergranular fracture feature

with a circle on the template. If one intergranular fracture feature extends

over several circles on the template, it shall be counted as one feature. The

intercepts from all of the photographs of each fracture surface shall be

totaled.

4.3.6.4.4 Testing Laboratory. When specified, the slow strain rate tensile test shall be done at the laboratory specified by the purchaser (see 6.2).

4.3.6.5 Acceptance criteria. The total number of intercepts counted in

4.3.6.4.3 for any fracture surface evaluated shall not exceed 100.

4.3.6.6 Rejection and retests. If any specimen fails to meet the requirements of this specification, the entire lot shall be rejected, subject to the retest provisions specified in 4.3.7.2.