PFI offers custom machining and fabrication services and works with numerous materials including aluminum, stainless steel, titanium, Inconel®, Monel® and Hastelloy®Listed below are the materials that PFI works with often, as well as some of their properties:
Aluminum is a soft, lightweight metal that normally has a dull, silvery appearance caused by a thin layer of oxidation that forms quickly when the metal is exposed to air. Aluminum oxide has a higher melting point than pure aluminum. Aluminum is nontoxic (as the metal), nonmagnetic, and non-sparking. It has a tensile strength of about 49 megapascals (MPa) in a pure state and 400 MPa as an alloy. Aluminum is about one-third as dense as steel or copper; it is malleable, ductile, and easily machined and cast.
It has excellent corrosion resistance and durability because of the protective oxide layer. Aluminum mirror finish has the highest reflectance of any metal in the 200-400 nm (UV) and the 3000-10000 nm (far IR) regions, while in the 400-700 nm visible range it is just beaten by silver and in the 700-3000 (near IR) by silver, gold, and copper. It is the second-most malleable metal (after gold) and the sixth-most ductile. Aluminum is a good heat conductor.
In metallurgy, stainless steel (inox) is defined as a ferrous alloy with a minimum of 10% chromium content.The name originates from the fact that stainless steel does not stain, corrode or rust as easily as ordinary steel. This material is also called corrosion resistant steel when it is not detailed exactly to its alloy type and grade, particularly in the aviation industry. As such, there are now different and easily accessible grades and surface finishes of stainless steel, to suit the environment to which the material will be subjected to in its lifetime.
Review the stainless steel surface finishes PFI can produce.
Common uses of stainless steel are the everyday cutlery and watchstraps. Stainless steels have higher resistance to oxidation (rust) and corrosion in many natural and man-made environments; however it is important to select the correct type and grade of stainless steel for the particular application.High oxidation resistance in air at ambient temperature is normally achieved with additions of a minimum of 13% (by weight) chromium, and up to 26% is used for harsh environments.The chromium forms a passivation layer of chromium(III) oxide (Cr2O3) when exposed to oxygen. The layer is too thin to be visible, meaning the metal stays shiny. It is, however, impervious to water and air, protecting the metal beneath. Also, when the surface is scratched this layer quickly reforms.
This phenomenon is called passivation by materials scientists, and is seen in other metals, such as aluminum. When stainless steel parts such as nuts and bolts are forced together, the oxide layer can be scraped off causing the parts to weld together. When disassembled, the welded material may be torn and pitted, an effect that is known as galling. Nickel also contributes to passivation, as do other less commonly used ingredients such as molybdenum and vanadium.
Duplex stainless steel
Called duplex because it has a two-phase microstructure consisting of grains of ferritic and austenitic stainless steel. When duplex stainless steel is melted it solidifies from the liquid phase to a completely ferritic structure. As the material cools to room temperature, about half of the ferrite grains transform to austenitic grains. The result is a microstructure of roughly 50% austenite and 50% ferrite.
The duplex structure gives this family of stainless steels a combination of attractive properties. Duplex stainless steels are about twice as strong as regular austenitic or ferritic stainless steels. And have significantly better toughness and ductility than ferritic grades. Duplex stainless steel, as with all stainless steels, the corrosion resistance depends mostly on the composition of the stainless steel. For chloride pitting and crevice corrosion resistance, their chromium, molybdenum and nitrogen content are most important. Duplex stainless steel grades have a range of corrosion resistance, similar to the range for austenitic stainless steels such as 304 or 316.
Duplex stainless steels show very good stress corrosion cracking (SCC) resistance, a property they have acquired from the ferritic side. SCC can be a problem under certain circumstances (chlorides, humidity, elevated temperature) for standard austenitics such as 304 and 316.
About 95% of titanium production is consumed in the form of titanium dioxide (TiO2), an intensely white permanent pigment with good covering power in paints, paper, toothpaste, and plastics. Paints made with titanium dioxide are excellent reflectors of infrared radiation and are therefore used extensively by astronomers and in exterior paints. It is also used in cement, in gemstones, as an optical opacifier in paper (Smook 2002), and a strengthening agent in graphite composite fishing rods and golf clubs. Recently, it has been put to use in air purifiers (as a filter coating), or in film used to coat windows on buildings which when exposed to UV light (either solar or man-made) and moisture in the air produces reactive redox species like hydroxyl radicals that can purify the air or keep window surfaces clean.
Because it is lightweight, has high tensile strength (even at high temperatures), extraordinary corrosion resistance, and the ability to withstand extreme temperatures, titanium alloys are used in aircraft, armor plating, naval ships, spacecraft, and missiles. It is used in steel alloys to reduce grain size and as a deoxidizer, and in stainless steel to reduce carbon content. Titanium is often alloyed with aluminum (to refine grain size), vanadium, copper (to harden), iron, manganese, molybdenum, and with other metals. Welded titanium pipe is used in the chemical industry for its corrosion resistance and is seeing growing use in petroleum drilling, especially offshore, for its strength and lightweight.
Inconel alloys possess several properties making them well suited for service in extreme environments. Inconel is very resistant to oxidation and corrosion. When heated, Inconel forms a thick, stable, passivating oxide layer, protecting it from further attack. Inconel retains strength over a wide range of temperatures. This makes it particularly attractive in high temperature applications where aluminum and steel would “soften”. Inconel’s high temperature strength is attained by solid solution strengthening or precipitation strengthening (depending on the alloy). In precipitation strengthening varieties, small amounts of columbium (niobium) combine with nickel to form the intermetallic compound Ni3Nb or gamma prime (γ’). Gamma prime forms small cubic crystals that inhibit slip and creep very efficiently at elevated temperatures.
Inconel is a difficult metal to shape using traditional techniques. It work hardens very quickly making it impossible to tap or thread with a die. External threads are machined using a lathe to “single point” the threads, or by rolling the threads using a screw machine. Holes with internal threads are made by welding or brazing threaded inserts made of stainless steel. Welding Inconel alloys may also prove difficult due to cracking and microstructural segregation of alloying elements in the heat affected zone. However, several alloys have been designed to overcome these problems.
Monel is a trademarked product comprising a series of rust-less (stainless) metal alloys, primarily composed of nickel (up to 67%) and copper, with some iron and other trace elements. It is resistant to corrosion and acids, and some alloys can withstand a fire in pure oxygen. It is commonly used in applications with highly corrosive conditions. Small additions of aluminum and titanium form an alloy with the same corrosion resistance, but with very high strength. Monel is used as the material for valve pistons in some higher quality trumpets, e.g., Bach Stradivarius. It is also often used for kitchen sinks and in the frames of eyeglasses. Its corrosion resistant characteristic makes it ideal for marine applications such as piping systems; pump impellers, trolling wire, and strainer baskets. Some alloys are completely non-magnetic and are used for anchor cable aboard minesweepers, housing magnetic field measurement equipment, and have applications in the oil drilling industry. Monel is typically much more expensive than stainless steel. Monel is very hard to machine as it work hardens instantly with heat and does not harden it.
Hastelloy is a trademark of Haynes International, Inc. The trademark is applied as the prefix name of a range of a number of highly corrosion resistant metal alloys loosely grouped under the material term “high-performance alloys”.
The predominant alloying ingredient is typically nickel. Other alloying ingredients are added to nickel in each of the subcategories of this trademark designation and include varying percentages of the elements molybdenum, chromium, cobalt, iron, copper, manganese, titanium, zirconium, aluminum, carbon and tungsten.
The primary function of the Hastelloy super alloys is that of effective survival under high-temperature, high-stress service in a moderately to severely corrosive, and/or erosion-prone environment where more common and less expensive iron-based alloys would fail, including pressure vessels of some reactors, distillation equipment, and pipes and valves in chemical industry.
Explosion Welded (Bonded) Material
Explosion welding is a solid-state (solid-phase) process where welding is accomplished by accelerating one of the components at extremely high velocity through the use of chemical explosives. Explosion welding was developed relatively recently (in the decades after World War II). However, its origins go back to World War I, when it was observed that pieces of shrapnel sticking to armor plating were not only embedding themselves, but were actually welded to the metal. Since the extreme heat involved in other forms of welding did not play a role, the conclusion was that the phenomenon was caused by the explosive forces acting on the shrapnel. These results were later duplicated in laboratory tests and, not long afterwards, the process was patented and put to use.
Explosion welding can produce a bond between two metals that are not necessarily welded by conventional means. The process does not melt either metal, instead it plasticizes the surfaces of both metals, causing them to come into intimate contact sufficient to create a weld. This is a similar principle to other non-fusion welding techniques, such as friction. Large areas can be bonded extremely quickly and the weld itself is very clean, due to the fact that the surface material of both metals is violently expelled during the reaction. Due to the nature of this process, producible geometries are very limited. Typical geometries produced include plates, tubing and tube sheets.
This process is most commonly utilized to clad carbon steel plate with a thin layer of corrosion resistant material like stainless steel, nickel alloy, titanium or zirconium.
PFI works regularly with carbon and low carbon steels, black iron, stainless, Inconel, Hastelloy and other alloy steels. Additionally, PFI has many years of experience in fabricating with exploded bonded material, most notably by using a bonded material of Inconel clad with nickel. The company forms them into reactors where the Inconel performs the need for strength and nickel provides corrosion resistance and reduces metal contamination.