Manufacturing Lecture 2

Properties of ceramic materials

-High hardness, electrical and thermal insulating, chemical stability, and high melting temperatures. -Brittle, virtually no ductility -Some ceramics are translucent, such as window glass (based on silica). -Include glass/china products, cutting tools, etc. -Can be made with the ceramic material in molten form or in powder form

Tool Steels

A class of (usually) highly alloyed steels designed for use as industrial cutting tools, dies, and molds. -To perform in these applications, they must possess high strength, hardness, hot hardness, wear resistance, and toughness under impact. -Tool steels are heat treated

Composite Materials

A materials system composed of two or more distinct phases whose combination produces aggregate properties different from those of its constituents. e.g. Cemented carbides (WC with Co binder), Plastic molding compounds with fillers, Rubber mixed with carbon black, and Wood (a natural composite as distinguished from a synthesized composite) -Fatigue properties are generally better than common engineering metals -Toughness is often greater -Possible to achieve combinations of properties not attainable with metals, ceramics, or polymers alone -Slow and costly to shape

Steel

An alloy of iron containing from 0.02% and 2.11% carbon by weight. May contain other alloying elements. Steel alloys can be grouped into four/five categories: Plain carbon steels, Low alloy steels, Stainless steels, Tool steels, Specialty steels

Thermosettling Polymers

Cannot tolerate repeated heating cycles as thermoplastics can. -When initially heated, they soften and flow for molding -Elevated temperatures also produce a chemical reaction that hardens the material into an infusible solid -If reheated, thermosets degrade and char rather than soften - e.g. Epoxies and certain polyesters

Plain carbon steel

Carbon is the principal alloying element, with only small amounts of other elements (about 0.5% manganese is normal). Its strength increases with carbon content, but ductility is reduced. High carbon steels can be heat treated to form martensite, making the steel very hard and strong.

Stainless Steel

Highly alloyed steels designed for corrosion resistance. Principal alloying element is chromium, usually greater than 15%, which forms a thin impervious oxide film that protects surface from corrosion. In addition to corrosion resistance, stainless steels are noted for their combination of strength and ductility.. While desirable in many applications, these properties generally make stainless steel difficult to work in manufacturing

Superalloys

High‑performance alloys designed to meet demanding requirements for strength and resistance to surface degradation at high service temperatures -Many superalloys contain substantial amounts of three or more metals, rather than consisting of one base metal plus alloying elements -Very expensive -Technologically important because of their unique properties

Ceramics

Inorganic compounds consisting of a metal (or semi‑metal) and one or more nonmetals. (e.g. Silica- silicon dioxide (SiO2), the main ingredient in most glass products, Alumina- aluminum oxide (Al2O3), used in various, More complex compounds such as hydrous aluminum silicate (Al2Si2O5(OH)4), the main ingredient in most clay productsapplications from abrasives to artificial bones)

Low Alloy Steels

Iron‑carbon alloys containing additional alloying elements in amounts totaling less than 5% by weight. Mechanical properties superior to plain carbon steels for given applications. Higher strength, hardness, hot hardness, wear resistance, and toughness, but heat treatment is often required to achieve these enhanced properties.

Nonferrous Metals

Metal elements and alloys not based on iron. (most important: aluminum, copper, magnesium, nickel, titanium, and zinc, and their alloys.) -Although not as strong as steels, certain nonferrous alloys have strength‑to‑weight ratios that make them competitive with steels in some applications

Two Phases of Composite Materials

Primary phase: Forms the matrix within which the secondary phase is imbedded Secondary phase: Imbedded phase sometimes referred to as a reinforcing agent, because it usually strengthens the composite material. The reinforcing phase may be in the form of fibers, particles, or various other geometries

Thermoplastic Polymers

Solid materials at room temperature, but viscous liquids when heated to temperatures of only a few hundred degrees -This allows them to be easily and economically shaped into products -They can be subjected to heating and cooling cycles repeatedly without significant degradation - e.g. Polystyrene and nylon

Metals

The most important engineering material. Their HIGH STIFFNESS and STRENGTH mean they can be alloyed for high rigidity, strength, and hardness. Their TOUGHNESS means they can absorb energy better than other classes of materials. They also have good electrical conductivity, good thermal conductivity (conduct heat better than ceramics or polymers), and competitively low cost.

Ferrous Metals

Those based on iron (e.g. steels, cast irons)

What is the purpose of alloying?

Through alloying, it is possible to increase strength, hardness, and enhance other properties compared to pure metals. Metal properties are also changed by strain hardening in cold working and by heat treatment.

Starting Forms of Metals used in Manufacturing Processes

1) Cast metal: starting form is a casting. 2) Wrought metal: the metal has been worked or can be worked after casting. 3) Powdered metal: starting form is very small powders for conversion into parts using powder metallurgy techniques

Polymers

A compound consisting of long‑chain molecules, each molecule made up of repeating units connected together -There may be thousands, even millions of units in a single polymer molecule -Word "polymer" is derived from the Greek words poly, meaning many, and meros (reduced to mer), meaning part -Most polymers are based on carbon and are therefore considered organic chemicals -Low density relative to metals and ceramics -Good strength‑to‑weight ratios for certain (but not all) polymers -High corrosion resistance, low electrical and thermal conductivity -Polymer products are made typically by shaping the material when it is in a heated and highly plastic state; common operations include extrusion and molding -Three types of polymers: Thermoplastic polymers (plastics), thermosetting polymers (plastics), and Elastomers (rubbers)

Cast Irons

Iron alloys containing from 2.1% to about 4% carbon and from 1% to 3% silicon. This composition makes them highly suitable as casting metals - Tonnage of cast iron castings is several times that of all other cast metal parts combined, excluding cast ingots in steel-making that are subsequently rolled into bars, plates, and similar stock. Overall tonnage of cast iron is second only to steel among metals