When fasteners are exposed to high temperatures they face several complications which affect their performance. One of the most common problems faced at elevated temperatures is rusting. In this post we will discuss some common problems faced by these fasteners, and material recommendations to address them.
The following are some of the common problems that affect the performance of fasteners at high temperatures:
Oxidation: This problem occurs at elevated temperatures. In an oxygen rich environment many metals will rapidly oxidize and start disintegrating. This problem can be avoided by selecting fasteners made from oxidation resistant alloys like: A-286: This is an iron – nickel – chrome – age hardened alloy which is valued for its’ excellent mechanical properties. This age-hardened alloy can maintain its’ strength as well as resist oxidation up to 1300 degree.
Weakening Material Strength: The material strength weakens at high temperature. This happens with most materials but there are many which can easily maintain their material strength at high temperatures such as: Nickel Alloys: Inconel alloys such as Inconel 625, 600, and 718 provide excellent oxidation resistance. These alloys can maintain their strength at elevated temperatures up to 2000oF, depending on the grade. Molybdenum: This refractory element is metallic and valued for its high tensile strength, toughness, and excellent wear resistance. Hence molybdenum fasteners are commonly used in fasteners for military and defense industry applications.
Vaporization at Extremely High Temperatures: Today, you will find many materials that are designed to withstand extremely high temperatures in vacuum furnaces. However many of them are known to rapidly oxidize or vaporize after a certain temperature limit. In such cases fasteners made from refractory elements are used. This is because refractory metals are known for their high melting points and ability to maintain their strength at temperatures as high as 2000 oF. The following are some of the popular refractory materials usually preferred for extremely high temperatures: Tantalum: This is one of the most common refractory metal in use today. Tantalum fasteners are valued for their excellent corrosion resistance, however, they are most preferred for their inertness or stability. Many manufacturers provide these fasteners in two configurations – pure tantalum fasteners, and tantalum with 2.5% tungsten. Tungsten: This metal has a low coefficient of thermal expansion, high melting points, lowest vapor pressures, as well as high tensile strength. These properties make tungsten fasteners ideal for vacuum furnace applications.
Extreme High-temperature Applications: As seen, all the above-mentioned fastener materials work excellent in certain temperature limits. However, none of them can withstand an upper temperature limit of 4000oF. Hence ceramic fasteners are considered ideal for such applications. Some of the popular materials available for your consideration include: Alumina: This is one of the common types of ceramic fasteners. This material is well known for its excellent hardness, wear-resistance, and electrical insulation properties. Zirconia: Yttrium stabilized Zirconia is well known for its properties – temperature stability and material strength. Zirconia fasteners are ideal for applications where additional strength is required.
All the above-mentioned considerations are valid for specific applications. If you are considering high-temperature fasteners for your next project, contact www.pvsipl.com