合金Alloy

合金中的相可以是固溶体、金属间化合物或它们的混合物。置换固溶体中溶质原子取代溶剂原子（如铜镍，休姆-罗瑟里规则要求原子半径差小于约 15%、晶体结构和电负性相近）；间隙固溶体中小原子（C、N、H）进入间隙（如钢中的碳）。溶质原子使晶格畸变、阻碍位错运动，所以合金通常比纯金属硬而强（固溶强化），但导电性降低。相图描述了不同成分和温度下合金的相组成。

Alloy phases may be solid solutions, intermetallic compounds or mixtures of them. In substitutional solid solutions solute atoms replace solvent atoms, as in copper–nickel; the Hume-Rothery rules require radii within about 15% and similar structures and electronegativities. In interstitial solutions small atoms such as C, N and H occupy interstices, as carbon does in steel. Solute atoms distort the lattice and hinder dislocations, so alloys are usually harder and stronger than pure metals (solid-solution strengthening) but conduct less well. Phase diagrams show which phases exist at each composition and temperature.

约公元前 3500 年两河流域开始使用青铜，中国商周青铜器（如后母戊鼎）铸造技艺精湛。《周礼·考工记》记载的“六齐”是世界最早的合金配比规律。钢的冶炼使铁器时代全面展开。1906 年维尔姆发现铝合金的时效硬化，制成杜拉铝用于飞艇和飞机。1913 年布里尔利发明不锈钢（含铬约 13%）。

Bronze came into use in Mesopotamia around 3500 BCE, and Shang and Zhou China cast bronzes of great skill, such as the Houmuwu ding. The 'six alloy formulas' recorded in the Kaogongji of the Rites of Zhou are the earliest known rules for alloy composition. Steelmaking carried the Iron Age forward. In 1906 Wilm discovered age hardening in aluminium alloys, giving duralumin for airships and aircraft, and in 1913 Brearley invented stainless steel with about 13% chromium.

碳钢和合金钢是用量最大的结构材料；不锈钢（Fe-Cr-Ni）因表面形成致密 Cr₂O₃ 钝化膜而耐蚀；铝合金和钛合金轻而强，用于航空航天；镍基高温合金用于涡轮叶片；焊锡（Sn-Ag-Cu）、形状记忆合金（Ni-Ti）、储氢合金（LaNi₅）和高熵合金各有特殊功能；14K、18K 金也是合金。

Carbon and alloy steels are the most used structural materials; stainless steels (Fe–Cr–Ni) resist corrosion thanks to a dense Cr₂O₃ passive film; aluminium and titanium alloys are light and strong for aerospace; nickel-based superalloys serve in turbine blades; solder (Sn–Ag–Cu), shape-memory alloys (Ni–Ti), hydrogen-storage alloys (LaNi₅) and high-entropy alloys have special functions; and 14- and 18-carat gold are alloys too.