Alloys as Certified Reference Materials (CRMs)

Abstract

Alloys are a mixture of pure metals and are mixed to improve their performance and properties. A summarized detail of numerous alloy systems is discussed in this chapter. Metal alloys are classified in two categories, ferrous and nonferrous. Different steels thus fall into the first category, and other popular alloys like brass, bronze, invar, duralumin, hindalium, etc. fall into the second category. However, any alloy or any material for that matter has to be checked for its quality, production, and performance repeatability, and thus a standardization protocol is necessary. Any such standardization involves checking and benchmarking the acceptable composition range of that material. Many of the properties of such alloys are further dependent on different crystalline phases of the individual metals when they are mixed – so these also deserve to be benchmarked. Additionally, the properties of alloys are also dependent on the thermal cycling processes, heat treatment procedures, and associated microstructure that they result in, i.e., on the thermodynamics of their preparation process. In some cases, it can also depend on the alloys’ resistivity and magnetic properties. In order to achieve repeatability in their preparation process, all of these need to be standardized, i.e., measured, quantified, and cataloged. Such a process will result in production of standard alloys or certified reference materials (CRMs). They may be compared with any subsequent batch to batch product for checking consistency of expected properties. Thus, different national metrology institutes (NMIs) all over the world have been working on standardizing different alloys of their interest for growth of their own economies. Here we shall summarize the different standard alloy samples available with the major NMIs of the developed world like NIST-USA, PTB-Germany, NMIJ-Japan, and NPL-UK or their surrogates. The American Society for Testing and Materials (ASTM) or American Iron and Steel Institute (AISI) or Society of Automotive Engineers (SAE) has independently developed an extensive database for a large number of alloys, irrespective of whether similar data has been published or not by any NMI. Consequently, for trade purposes, several alloy makers from all over the world follow these standard data in situations where NMIs do not have specific standards of interest. A summarized discussion on all of them shall be made along with their consequences on their economies in this chapter. In the case of emerging economies like NMI-India, irrespective of what other NMIs have or have not worked on, this write up discusses how any alloy as a case study can be successfully standardized. It shall be worth the effort as that knowledge may be commercially exploited for the local and global market and extrapolated for making of other alloy standards and quality alloys in due time.