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Metal Testing Laboratory

Metals make up almost 75% of all the elements in the Periodic Table, and vary widely in strength, density, corrosion resistance, melting point, electrical conductivity, and other properties. However, almost all of these properties can be altered by adding various amounts of other elements, and some characteristics can be changed by different processing methods.  The possibilities are almost endless, which explains why metals can be made into so many products, from aircraft carriers to computer chips. 

Iron is a perfect example of these endless possibilities. Although many people think of iron as a relatively new discovery, iron was used in tools and weapons as early as 4000 BC.  Pure iron is not as strong as steel, but it is very ductile, which allows it to be hammered into many useful shapes. However, it was not until 500 BC that the process was discovered for changing iron into steel. Strangely, when iron contains more than about 3% carbon, it is not designated steel, but rather cast iron. Iron is considered to be steel only if carbon content is less than about 2%.  

Steels

Today, steels include carbon steel, silicon steel, stainless steel, tool steel, high-temperature steel, high-strength steel, duplex steel, and literally thousands of variants. In addition, they may be cast, wrought, forged, or made via powder metallurgy techniques. They may also be heat treated, coated, or given a variety of surface treatments. As examples, consider carbon steel, silicon steel, and stainless steel.

  • Carbon steels, also called mild steels, are defined as those steels with no more than 0.3% carbon, and they account for 90% of steel production.  They serve as the structural steel beams in buildings, and form most of the structures in automobiles. High-strength/low-alloy steels have small additions of manganese, typically about 1.5%, to increase strength without increasing cost significantly.
  • Silicon steels, also called electrical steels, contain up to 3% silicon. They are easily magnetized, and are used in generators, transformers, motors, and other electrical applications. Silicon additions promote optimal orientation of the grain structure. During the rolling operation,  grain-oriented steels are given mill treatments designed to yield exceptionally good magnetic properties in the rolling  direction.  
  • Stainless steels contain chromium in amounts ranging from 11% to about 30%. The chromium forms an adherent, protective chromium oxide film on the surface that prevents corrosion. These alloys are widely used in the chemical, pharmaceutical, marine, and power-generation industries.  In addition to chromium, advanced stainless steels may contain other elements added to improve particular characteristics. These include nickel, molybdenum, copper, titanium, aluminum, silicon, niobium, nitrogen, sulfur, and selenium.

Although physical and mechanical properties of steel may be changed by adding other elements, properties may also be changed by various processing methods. Forging is one such method: By repeatedly impacting a cast material heated to red-hot, toughness is greatly improved. Another important process is heat treating, a family of processes involving heating the steel to a certain temperature in a vacuum or a gas such as ammonia, then cooling the steel either slowly or quickly, in air or water or oil. By careful selection of the parameters, properties such as hardness and toughness can be tailored.

Because of the wide variations in composition, microstructure, and processing, the experienced NSL team analyzes steel products for chemistry, characterizes microstructure, and tests for the physical and mechanical properties appropriate for the specific service environment.

Superalloys

Superalloys are based on nickel, iron-nickel, and cobalt, and are designed to have enough strength and corrosion resistance to function at temperatures above 1000°F. They are complex alloys that include additional elements such as aluminum, chromium, titanium, tungsten, rhenium, and/or tantalum, among others. Different elements are added for specific properties such as corrosion resistance in chemical plants, or high-temperature resistance in gas turbine engines.

In addition to alloying elements, advanced processing techniques such as directional solidification and single-crystal casting are critical for improved ductility and resistance to creep and fatigue at high temperatures.

Because these alloys function for long periods at high temperatures, complete characterization requires testing for creep rupture strength, fatigue strength, and fracture toughness. Depending on the application, we also test for coefficient of thermal expansion, density, and melting range. In addition, because superalloys are often coated, we analyze the coating for composition, hardness, thickness, and adherence.

Aluminum

Aluminum is low in density, ductile, and corrosion-resistant, and it can be rolled, cast, or extruded into complex shapes. Aluminum can be alloyed with copper, magnesium, silicon, zinc, and other elements. Some alloys are almost as strong as steel, while others are malleable enough to be formed into foil. Aluminum has excellent electrical conductivity, and some alloys serve as miles-long electric transmission lines. Mechanical and physical characteristics depend on both alloying elements and process technology.

Some alloys are designed for casting, while others are designed for extrusion. Aluminum alloys are frequently anodized,  and others are heat treated. When characterizing aluminum, NSL checks for porosity in castings, and analyze extrusions, forgings, rolled products, and heat-treated parts for mechanical and physical properties expected of the specific alloy and its process history. 

Metals for electronics (copper, precious metals, gallium, silicon, arsenic, and solder alloys)

Copper provides excellent electrical and thermal conductivity, corrosion resistance, malleability, and fatigue resistance in electronic devices such as printed circuit boards, connectors, semiconductor packages, and lead frames. For example, printed circuit boards are made by laminating thin sheets of copper to an insulating nonconductive substrate, then etching away the unneeded copper, leaving only the copper trace. Copper is also inside the vias, the vertical holes between layers of substrate that connect the various circuit components. On printed circuit boards, NSL analyzes the copper traces and vias for breaks, porosity, contaminants, short circuits, and other flaws by thermal imaging, scanning electron microscopy, optical microscopy, and other techniques.

Precious metals such as gold, silver, palladium, and platinum are also important electrical conductors, serving as contacts, connectors, and coatings for many devices. In these applications, we test for mechanical properties, dimensional measurements, chemical composition, electrical conductivity, and grain size of the various materials.

Gallium is a soft silvery metal that is a brittle solid at low temperatures. Arsenic is classified as a metalloid, an element with characteristics similar to both metals and nonmetals. These two materials are combined to form gallium arsenide, a semiconductor ubiquitous in electronic devices.  Silicon and germanium are also metalloids and semiconductors that are widely used in electronics. Most solder materials today are nominally free of lead, and most contain some combination of tin, copper, silver, bismuth, indium, zinc, and/or antimony. NSL analyzes all of these materials for compliance with WEEE and RoHS directives, and tests for correct chemistry, mechanical properties, and physical characteristics. 

Titanium

Titanium is available as “commercially pure” and as a wide range of alloys designed for a variety of applications. Its combination of high strength-to-weight ratio, outstanding mechanical properties, and excellent corrosion resistance makes titanium the material of choice for many critical applications in jet engines, aerospace structures, chemical process equipment, and medical implants. Advanced titanium materials such as titanium composites and titanium aluminides have unique properties and specialized applications.

Although titanium is available in typical mill forms such as of billet, bar, and sheet, its high cost has led to development of several net shape technologies, especially castings.  Superplastic forming/diffusion bonding has also become a commercial production method. Several net-shape additive manufacturing technologies based on powder metallurgy are being commercialized and/or are under development to reduce waste and eliminate the need for tooling. Examples of this technology include direct metal laser sintering, electron beam melting, and laser-engineered net shapes.

Regardless of fabrication method, titanium components typically serve in critical applications and must meet very strict standards for mechanical properties, and very tight tolerances for chemical composition. NSL analyzes for composition (including trace elements) and microstructure, and tests for hardness, tensile and impact strength, porosity, melting range, and chemical resistance. We also provide particle size and particle size distribution testing. 

Zirconium and Hafnium

Zirconium is a greyish-white lustrous metal that is very strong, malleable, corrosion-resistant, and capable of functioning very high temperatures. Zirconium is widely used in the chemical process industry because of its excellent resistance to hot sulfuric acid. It is almost transparent to thermal neutrons; therefore, one of its major applications is cladding for uranium fuel rods and other nuclear reactor components. Because it is compatible with the human body, it is used in medical applications such as surgical instruments and implants. Zirconium is also an alloying element for many metals, including superalloys, aluminum, copper, and others.

Hafnium is always present in zirconium ores, and it is similar in that it is highly reactive, very strong and malleable, and has high corrosion resistance. However, its melting point is a thousand degrees higher at 4051ºF, and its density is twice that of zirconium at 13.3 g/cm3.  Although zirconium is almost transparent to thermal neutrons, hafnium absorbs them, enabling it to act as control rods in nuclear reactors.  In addition, its extreme hardness enables applications in rocket thruster nozzles, welding tips, and plasma cutting torches. It is added to superalloys as a grain-boundary strengthener, and to many other alloy systems to increase strength and corrosion resistance.

Refractory Metals

Refractory metals have the highest melting temperatures of all the metals, except for osmium and iridium, which are members of the platinum group. Refractory metals include columbium (niobium), tantalum, molybdenum, tungsten, and rhenium. In spite of their high melting temperatures (all are above 3600°F), they are generally not suitable for high-temperature service because they corrode at moderate temperatures in oxidizing atmospheres. Therefore, they are frequently coated to enable service at high temperatures. Rhenium differs from the other refractory metals in that it remains ductile from subzero to high temperatures, with an elastic modulus second only to those of iridium and osmium.

NSL tests refractory metal parts for wear, corrosion, and hardness. Depending on the application, we also test for fracture toughness, stress-rupture strength, tensile strength, and other properties.

Zinc

Zinc and its alloys are readily cast and wrought, and zinc is also an effective corrosion prevention coating for steel. Zinc alloys are cast by almost every method, including die casting, sand casting, investment casting, centrifugal casting, and many others. Impurity limits are very important for zinc alloys, because low mechanical properties and reduced corrosion resistance can be the result.

Lead

Lead is primarily used in lead-acid storage batteries, solders, cable sheathing, and construction.  It provides sound and vibration damping and radiation shielding, and serves as an alloying element to improve machinability of steel and copper.

Rare earths

The rare earth elements include the fifteen lanthanides plus scandium and yttrium, which are considered rare earth elements because they are typically found in the same ore deposits and have similar chemical properties. At NSL, the rare earths we most frequently encounter are samarium and neodymium, which are found in samarium-cobalt and neodymium-iron-boron magnets. 

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NSL metals testing and analysis capabilities

MECHANICAL PROPERTIES

PHYSICAL PROPERTIES

METALLOGRAPHY

NONDESTRUCTIVE TESTING

Hardness (Brinell, Rockwell, Micro)

Specific heat

Specimen saws

Inductively coupled plasma/mass spectrometry

Tensile strength

(room and elevated temperature)

Coefficient of thermal expansion

Sample polishing equipment

Inductively coupled plasma/Auger electron spectroscopy

Charpy impact strength

Electrical conductivity

Mounting tools

Image analysis

Fracture toughness

Thermal conductivity

Etching equipment and chemicals

X-ray fluorescence

Compression strength

Corrosion resistance

Optical microscope

Optical comparator

Bend testing

Particle size

Stereo microscope

Laser diffraction

Elongation

Density

Scanning electron microscope

Optical emission spectrometer

Stress rupture strength

Weldability

Image analysis instruments and software

Surface analysis

Elastic modulus

 

Particle size analysis

Atomic absorption

Process and specimen preparation equipment

  • Heat treating furnace
  • Lathes and other machining equipment
  • Forge
  • Casting furnace

NSL also provides a complete range of chemical analyses.