Precipitation hardening

Precipitation hardening, also called age hardening or particle hardening, is a <a href="/facts/Heat_treatment/xR2tVyTU">heat treatment</a> technique used to increase the <a href="/facts/Yield_(engineering)/mrSg02gW">yield strength</a> of <a href="/facts/Malleable/SBJsahEk">malleable</a> materials, including most structural alloys of <a href="/facts/Aluminium/7wmR8jYE">aluminium</a>, <a href="/facts/Magnesium/XyIhd2FG">magnesium</a>, <a href="/facts/Nickel/KwMCHYRP">nickel</a>, <a href="/facts/Titanium/53ArnDoy">titanium</a>, and some <a href="/facts/Steel/aN6qWo4H">steels</a>, <a href="/facts/Stainless_steel/IDdo8bEx">stainless steels</a>, and <a href="/facts/475_%C2%B0C_embrittlement/W8QVQUp1">duplex stainless steel</a>. In <a href="/facts/Superalloys/UwshApNV">superalloys</a>, it is known to cause <a href="/facts/Yield_strength_anomaly/RkQwvdnt">yield strength anomaly</a> providing excellent high-temperature strength. 
Precipitation hardening relies on changes in solid <a href="/facts/Solubility/kLE9h3Jb">solubility</a> with <a href="/facts/Temperature/QyGe4gmj">temperature</a> to produce fine particles of an impurity <a href="/facts/Phase_(matter)/NkHXDdN3">phase</a>, which impede the movement of <a href="/facts/Dislocation/m1tkJYIq">dislocations</a>, or defects in a <a href="/facts/Crystal/e2R2mk3E">crystal</a>'s <a href="/facts/Crystal_structure/bJ4bCeHd">lattice</a>. Since dislocations are often the dominant carriers of <a href="/facts/Plasticity_(physics)/2VKo6keA">plasticity</a>, this serves to harden the material. The impurities play the same role as the particle substances in particle-reinforced composite materials. Just as the formation of ice in air can produce clouds, snow, or hail, depending upon the thermal history of a given portion of the atmosphere, <a href="/facts/Precipitation_(chemistry)/s3BgsLLY">precipitation</a> in solids can produce many different sizes of particles, which have radically different properties. Unlike ordinary <a href="/facts/Tempering_(metallurgy)/Vn3fcFBH">tempering</a>, alloys must be kept at elevated temperature for hours to allow precipitation to take place. This time delay is called "aging". Solution treatment and aging is sometimes abbreviated "STA" in <a href="/facts/Specification/xEMUsktp">specifications</a> and <a href="/facts/Product_certification/fblgj9g4">certificates</a> for metals.
Two different heat treatments involving precipitates can alter the strength of a material: solution heat treating and precipitation heat treating. <a href="/facts/Solid_solution_strengthening/lJAJ4HVe">Solid solution strengthening</a> involves formation of a single-phase solid solution via quenching. Precipitation heat treating involves the addition of impurity particles to increase a material's strength.

Precipitation hardening open-in-new

Precipitation hardening