1.2 METALS 10 What metals are used most in engineering? An alloy is a substance made by melting two or more elements together, and at least one of them is a metal. The components of alloys cannot be separated using a physical means. Examples of refractory metals are: molybdenum, tungsten, chromium, iridium, rhodium. Superalloys are highstrength, complex alloys that are resistant to high temperatures, severe mechanical stress and have high surface stability. They are used, for example, in the turbine section of jet engines. alloy: lega to arrange: combinare, sistemare carbon steel: acciaio al carbonio concern: preoccupazione concrete: calcestruzzo stainless steel: acciaio inossidabile thermoset: termoindurente tool steel: acciaio per utensili 28 GENERAL CHARACTERISTICS OF METALS General description of materials There are thousands of materials used in engineering applications and most of them belong to one of the three main classifications: metallic, ceramic, polymeric. Additionally, different materials can be combined to create a composite material. Materials are often organised into groups based on their chemical composition or certain physical or mechanical properties; composite materials are often grouped by the combination of materials or how they are arranged together: Metals Polymers Ferrous metals and alloys (irons, carbon steels, alloy steels, stainless steels, tool steels) Non-ferrous metals and alloys (aluminium, copper, magnesium, nickel, titanium, precious metals, refractory metals , superalloys ) Thermoplastics plastics Ceramics Composites Glasses Glass ceramics Graphite Diamond Reinforced plastics Metal-matrix composites Ceramic-matrix composites Sandwich structures Thermoset plastics Elastomers Metals Metals represent about two thirds of all the elements and about 24% of the mass of the planet. Metals have useful properties including strength, ductility, high melting points, thermal and electrical conductivity, and toughness. Some of the common metallic materials and their typical uses are: Iron/Steel: steel alloys are used for critical strength applications; Aluminium and its alloys: they are used because they are easy to form, easily available, inexpensive, and recyclable; Copper and its alloys: they have a number of properties that make them useful, including high electrical and thermal conductivity, high ductility, and good corrosion resistance; Concrete Titanium: titanium alloys are used for strength in higher temperature (~540°C) applications, when weight is a concern, or good corrosion resistance is required; Nickel: nickel alloys are used for even higher temperature (~810-1100° C) applications or when good corrosion resistance is required; Refractory metals: they are used for the highest temperature (> 1100° C) applications. Materials MechPower.indb 28 30/01/24 17:07