PROCESSING and PROPERTIES 5/25/2018 5/25/2018 PROCESSING and PROPERTIES © 2007 Microsoft Corporation. All rights reserved. Microsoft, Windows, Windows Vista and other product names are or may be registered trademarks and/or trademarks in the U.S. and/or other countries. The information herein is for informational purposes only and represents the current view of Microsoft Corporation as of the date of this presentation. Because Microsoft must respond to changing market conditions, it should not be interpreted to be a commitment on the part of Microsoft, and Microsoft cannot guarantee the accuracy of any information provided after the date of this presentation. MICROSOFT MAKES NO WARRANTIES, EXPRESS, IMPLIED OR STATUTORY, AS TO THE INFORMATION IN THIS PRESENTATION. 1

Intrinsic properties such as strength and resistivity depend on the microstructure and microstructure depends on processing The ability to tune microstructure and properties is central to materials processing and design, so it brings with it the need for good process understanding and control

The figure depicts the process history of an aluminum bike frame Materials processing involves more than one step Each process step has a characteristic thermal history Designers should watch out for unintended side-effects in the joining stage Design focuses on the properties of finished products, but some of these properties are also critical during processing

Metals Glasses and Ceramics

Polymers and Elastomers The role of shaping processes is to produce the right shape with the right final properties The first is achieved by controlling viscous flow or plasticity The second requires control of the nature and rate of microstructural evolution

Phase: regions of a material with a specified atomic arrangement Phase diagram: maps showing the phases expected as a function of composition and temperature, if the material is in its lowest free energy state Phase transformation: occur when the phases present change – requires a driving force and a mechanism

The diagram divides up into single- and two- phase regions, separated by grain boundaries At any point in the two-phase region, the present phases are those found at the phase boundaries at either end of the horizontal tie-line through the point defining the composition and temperature concerned Both lead and tin will dissolve in one another to some extent, with the maximum solubility in both cases being at the same temperature The pure elements have a unique melting temperature Alloys show a freezing range between the boundaries known as the liquidus and solidus, so there is no longer a single melting point At the eutectic point, the alloy can change from 100% liquid to 100% two-phase solid

Pure iron shows three phases in the solid state - As the temperature increases, iron changes from α-iron (BCC) to γ- iron ( FCC) to δ-iron (BCC) and then melts The single-phase austenite field has a eutectoid point at its base – at this point the single-phase austenite at a composition of 0.8 wt% C can transform on cooling to a mixture of ferrite and cementite The austenite field closes at the top in a peritectic point at which single-phase austenite wit this composition transforms on heating to a mixture of liquid and δ-iron

When a liquid solidifies, solid first has to appear from somewhere, after which the interface between solid and liquid can migrate to enable atom to switch from one phase to another at the boundary The two stages of solidification are nucleation and growth

Most alloys offer both cast and wrought variants Metals with an HCP structure such as Cu, Ti, and Ni are primarily cast at high temperatures because of their inherent lack of ductility Casting and wrought alloys in a given system tend to have different compositions Casting leads to coarser microstructures and poorer strength and toughness than a wrought alloy Good castability requires higher levels of alloying additions than wrought alloys to lower the melting temperature

In casting, a liquid above its melting point is poured into a mold where it cools by thermal conduction – it is relatively cheap and well suited for complex 3-d shapes New solid forms by nucleation – new crystals form in the melt, on the walls of the mold, or on foreign particles Crystals grow in opposing directions and impinge on one another to form grain boundaries

Deformation processes influence microstructure by various means Deformation processes exploit the plastic response of metals, that is, their ability to remain intact without damage when subjected to large strains and shape changes Deformation processes influence microstructure by various means Temperature – determines the phases present and is relevant during forming and cool-down Grain size – forming process can strengthen the metal by changing both the size and shape of the grains

Forming processes, while increasing the strength of metals, often reduce their ductility It is often necessary to follow forming with an annealing heat treatment to restore some of the materials ductility

In a typical heat treatment, a component is heated to high temperature, cooled at a controlled rate, and usually reheated to an intermediate temperature The figure illustrates the thermal profile and resulting microstructure for a heat treatment process A solid solution is formed at high temperature followed by precipitation hardening at an intermediate temperature after being cooled

Normalizing Quench and temper Slow cooling from high temperature producing a microstructure of lower strength but high toughness No follow-up heat treatment Quench and temper Cooled faster than the critical cooling rate producing a martensitic microstructure with high strength and low toughness Then reheated at an intermediate temperature to restore toughness

Thermal welding of metals involves heating and cooling which may cause phase transformation in the weld metal and in the heated regions of the weld The figure shows a weld cross- section with corresponding thermal histories in the weld metal and heat-affected-zone On the right are typical hardness profiles induced across welds in various metals

Surface treatments exploit many different mechanisms and processes to change the surface microstructure and properties Laser hardening is a surface treatment process that modifies microstructure – the traversing laser beam induces a rapid thermal cycle, causing phase changes on both heating and cooling – the track below the path of the laser has a different microstructure of high hardness

Structural sections are commonly made from wrought plain carbon steel that has undergone significant deformation processes The microstructure consists of ferrite and pearlite which produces high fracture toughness and strength

The main alloying element in stainless steel is chromium – nickel as also frequently used The addition of chromium imparts excellent corrosion resistance to the steel while nickel and chromium provide solid solution hardening

Strength and toughness tend to dominate the property profile desired for applications that use ferrous metals The range of mechanical properties able to be achieved through alloying and processing makes ferrous metals the most versatile group of engineering materials

Glasses and Ceramics Because of their susceptibility to cracking, defect control is the most important aspect of processing glasses and ceramics – while some thermal processes can increase the properties of glasses, changes in composition is generally used to alter the properties of ceramics Ceramics can be shaped by filling a mold with loose powder and compacting it – the main microstructural evolution is the shrinkage of porosity during compaction

Processing can play a significant role in determining the final molecular arrangement and thus properties if the molecules are first aligned mechanically by the flow induced during the shaping process, and cooling is rapid enough to freeze the alignment The most dramatic impact of processing on polymer properties is in making fibers Drawing fibers creates significant molecular alignment and the covalent bonding along the chain is exploited to markedly increase the specific strength and stiffness of the polymer

Hybrid materials offer material property profiles not found for single materials However, many processing challenges are presented when shaping and joining hybrids

SUMMARY Manufacturing processes are key to producing materials with the desired properties Processes affect the microstructure of the material Surface processing can add additional properties such as wear or corrosion resistance Joining processes can introduce changes in the strength of the object because joints have different strengths than the raw material. Metals are the most important engineering material to provide a range of strengths and toughness Ceramics, glasses and polymers can also be modified through: blending Cross linking