The subject of high-temperature alloys encompasses both cast and wrought products that are available from a number of qualified suppliers. The intent of this article is to provide a simplified overview of the basic requirements necessary for selection of alloy systems for use in thermal processing applications running from - 320˚F (-195˚C) to 2250˚F (1225˚C) and beyond.

The information is presented for the purpose of aiding those in the selection process who have not had the opportunity to work with these alloys in great detail. More detail can be obtained from a number of sources and standards from organizations such as SAE International (www.sae.org), ASTM International (www.astm.org) and the Alloy Casting Institute to name a few. There are many other sources of technical and research information specific to a given application such as from the many suppliers of these materials. By Dan Herring

Hardness, as applied to most materials and in particular metals, is a valuable, revealing and commonly employed mechanical test that has been in use in various forms for more than 250 years.

As a material property, the value and importance of hardness cannot be overstated. The information from a hardness test can be used to provide critical material performance information and insight to the durability, strength, flexibility and capabilities of a variety of component types from raw materials to prepared specimens and finished goods. Hardness testing is widely used in a multitude of industries and is particularly significant in structural, aerospace, automotive, quality control, failure analysis and many other forms of manufacturing. What is indentation hardness testing? The most basic and commonly used definition is the resistance of a material to permanent (plastic) deformation. It is measured by loading an indenter of specified geometry and properties onto the material for a specified length of time and measuring either the depth of penetration or dimensions of the resulting indentation or impression. Rockwell® testing is the most commonly used method by virtue of the quick results generated and is typically used on metals and alloys. It generates a value based on indentation depth or unrecovered indentation. By Bill O'Neill

The latest material and process developments for refractory metals are discussed. Learn how proper hot-zone design leads to improved performance and productivity.

Metals that offer a higher melting point than platinum (3222°F/1772°C) are generally considered to be refractory metals (Ru, Rh, Os, Ir, Pt, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Tc, Re). For functional components in furnace construction, only molybdenum- (Mo), tungsten- (W) and tantalum- (Ta) based materials are of significant importance. For several decades these materials have been fabricated and utilized for heating elements, radiation shielding and mechanically loaded furnace fixtures. The following properties, and their synergistic effects, highlight why refractory metals are frequently chosen for such high-temperature applications: By Mike Ferullo & Bernd Kleinpass

Manufacturers sometimes impose tight Rockwell hardness specifications on themselves in an attempt to improve quality. Other times heat treaters are asked by customers to meet tightly controlled limits such as +/-1.0 Rockwell point. Are these tight limits realistic, and do they have any real product benefit?

As manufacturers strive to increase the quality of the products they produce, there is a corresponding need to improve the accuracy of the measurements used to control or monitor the product’s quality. Rockwell hardness testing is one of those measurements. In an effort to reduce the variations in the performance of their products, some users are attempting to hold the Rockwell results on critical parts to +/-1.0 Rockwell point. This article will discuss the realities of trying to hold such a tight tolerance and will provide some insight on how to do it. By Ed Tobolski

Different combinations of properties can be produced by varying the heat treatment of copper and its alloys—influencing strength, hardness, ductility, conductivity, impact resistance, and inelasticity.

Common heat treatments applied to copper and its alloys are:

1) Homogenizing to reduce chemical segregation and coring of cast structures, and create a more uniform structure in hot worked materials. 2) Annealing to soften work hardened (strain-hardened) materials. 3) Stress relief to stabilize properties and improve strength and dimensions particularly for cold worked parts, and to reduce residual stress. 4) Solution treating and precipitation (age) hardening to provide increased strength by precipitation of constituents from solid solution. 5) Quenching hardening by a martensitic-like transformation followed by tempering.

Copper and copper alloys are supplied in the solution treated condition, in the solution treated and cold worked condition, and in the age-hardened condition. Their heat treatment falls into two general categories: hardening either by low temperature precipitation treatments or hardening by quenching from elevated temperature. By Dan Herring

Everyone knows how to perform a hardness test, or do they? Hardness testing is made more complex by such real world factors as a hard case over a soft core, hard particles, soft inclusions, and soft layers over hard cores to name a few. Part size, shape, and weight are other test challenges. Selection of the best test method, use of proper procedures, and a keen awareness of what and where to test are needed.

Hardness testing is one of the most common quality control checks performed. It is often used to determine the success or failure of a particular heat treatment operation or to understand the material’s current condition. Hardness testing is one of the easiest tests to perform on the shop floor or in the laboratory, but it can be one of the hardest tests to do properly. By Alan Stone and Daniel H. Herring.

Ion nitriding can be used in many applications, but some are so unique that they can be called “the best” applications, where the competitive treatments such as salt bath and gas nitriding cannot easily duplicate the unique results of ion nitriding.

Ion, or plasma, nitriding has been studied and used industrially for more than 40 years [1-8], but the technology has not been used to its full potential. Ion nitriding/nitrocarburizing is a low temperature (800-1100˚F, or 430-595˚C) process, which results in little or no distortion of the treated parts even if significant residual compressive stress is induced to the surface layer of the treated products. The ion nitriding process also has been referred to by other surface treating characteristics including plasma, vacuum, diffusion, low nitriding potential, passive surfaces activating, easy-to-control structure and pollution-free processes. These process characteristics with the exception of the low nitriding potential concept are discussed in the literature. By E. Rolinski and G. Sharp