When fasteners are exposed to high temperatures, they face several complications that affect their performance. One of the most common problems faced at high temperatures is rust. In this article, we'll discuss some of the common problems faced with these fasteners, along with material recommendations to address them.
Fasteners for specific high temperature concerns
The following are some common issues that affect fastener performance at elevated temperatures:
Oxidation: This problem occurs at high temperatures. In an oxygen-rich environment, many metals oxidize rapidly and begin to break down. This problem can be avoided by choosing fasteners made from oxidation resistant alloys such as:
A-286: This is an iron-nickel-chromium age hardenable alloy valued for its excellent mechanical properties. This age hardenable alloy retains its strength and resists oxidation up to 1300 o
Weakening of material strength: Material strength weakens at high temperatures. This happens with most materials, but there are many materials that easily maintain their material strength at elevated temperatures, such as:
Nickel Alloys: Inconel alloys such as Inconel 625, 600 and 718 have excellent oxidation resistance. These alloys can maintain their strength at high temperatures up to 2000 o F, depending on the grade.
Molybdenum: This refractory element is metallic and valued for its high tensile strength, toughness, and excellent wear resistance. Therefore, molybdenum fasteners are commonly used in fasteners for military and defense industry applications.
Vaporization at Extremely High Temperatures: Today you will find many materials designed to withstand extremely high temperatures in vacuum furnaces. However, many of them are known to oxidize or evaporate rapidly after certain temperature constraints. In this case, fasteners made of refractory elements are used. This is because refractory metals are known for their high melting points and ability to retain strength at temperatures as high as 2000 o F. Here are some popular refractory materials that are often preferred for extremely high temperatures:
Tantalum: This is one of the most commonly used refractory metals today. Tantalum fasteners are valued for their excellent corrosion resistance, but are preferred for their inertia or stability. Many manufacturers offer 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 point, lowest vapor pressure, and high tensile strength. These properties make tungsten fasteners ideal for vacuum furnace applications.
Extreme High Temperature Applications: As you can see, all of the above fastener materials perform well within specific temperature ranges. However, none of them can withstand the upper temperature limit of 4000oF. Therefore, ceramic fasteners are considered ideal for such applications. Some popular materials for your consideration include:
Alumina: This is a common type of ceramic fastener. This material is known for its excellent hardness, wear resistance and electrical insulation properties.
Zirconia: Yttrium stabilized zirconia is known for its properties - temperature stability and material strength. Zirconia fasteners are ideal for applications that require extra strength.