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SELECTION OF MATERIALS FOR ENGINEERING APPLICATIONS

Materials 7

SELECTIONOF MATERIALS FOR ENGINEERING APPLICATIONS

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Materialselection isan importantprocess in the design process of any engineering part or assembly. Inthe context of engineering productdesign,the main aim of material selection is to reduce the cost, while stillmeeting the product projected performance (Ashby2011).A systematic selection of material for a specific engineeringapplication normally starts with the cost and properties of thematerial. The material used for production of an engineering productaffects the performance,quality, life, etc., of the product (&quotAdvancedEngineering Materials – Wiley Online Library&quot, 2016).Therefore, it becomes very necessary to select the best and suitableengineering materials for a successful product. Normally, severalfactors are considered when selecting engineering materials forvarious engineering applications. The major factors include thematerial’s availability, mechanical strength, ductility, stability,fabricability, design, corrosion resistance, and cost (McNaughton2015).&nbsp

Thereare many engineering materials available in the market. This reportfocuses on steel as an engineering material. Steelis an alloy of many metals. It is a mixture of iron, carbon, andother metals in certain percentages. Normally, the percentage ofcarbon in steel ranges between 0.02 % and 1.7 % of the total weight.The amount of carbon in a steel determines the name of the steel. Forinstance, a steel alloy with more than 1.7% of carbon by weight isreferred to as a cast iron. The purpose of alloying iron with otherelements to form steel is to introduce certain mechanical and otherproperties that cannot be achieved in a pure iron.For example, an alloy of steel is much stronger than wrought iron,which does not contain carbon element. Different types of steel areused in different engineering applications (Ashby2011).&nbsp

Theaim of this report is to suggest the most suitable material for thevarious engineering products such as cutting tools, rail trackpoints, cutlery or surgical instruments, and the turbine blades.

Factorsfor Material Selection

Themajor factors that are considered during material selection arediscussed below.

Availability

Beforean engineer settles for a particular engineering material, itimportant that they consider the availability of the material. Thematerial chosen for an engineering part or product should be easilyavailable at an appropriate cost and in the desired form.The availability of material also determines its cost. Therefore, anengineer`s choice should be dictated by this factor so that the partor product is manufactured in the most economical manner. Engineeringmaterials are normally available in various forms such as rolledsheets, forging, casting, among others forms. However, theavailability of an engineering material in a suitable form is ofimportance to facilitate the production of the product with thedesired quality (Barrett, Nix, and Tetelman 2013).&nbsp

MechanicalStrength

Themechanical strength of an engineering material is an importantcriterion in material selection for any engineering product orapplication. Mechanical strength can be defined as the ability of anengineering material to withstand forces or loading conditions.Materials chosen for an engineering application should possess anappropriate mechanical strength to be able to withstand forces andloads that may be developed in the product during the actualoperation (Mendesand Lago 2014).&nbsp

Ductility

Ductilityof an engineering material is a mechanical property of a materialthat makes it suitable for by extrusion, drawing, rolling, and otherengineering processes that depend on a material`s ability to flow.Basically, ductility is defined as the ability of an engineeringmaterial to flow or strength plastically without failure or breaking(Askeland 2014).&nbspDuctilityof a material can be related to the mechanical strength of thematerial. Substantial ductility can be achieved at the sacrifice of amaterial’s mechanical strength and vice versa. For instance, whenthere is an increase in temperature, material’s ductility increasesand the strength decreases. During cold rolling processes, themechanical strength of material is increased while its ductility isconsiderably decreased. It is not always necessary that a materialused for an engineering application to possess high ductility.However, the material should possess suitable ductility, depending onthe intended fabrication process (Callister 2012).&nbsp

Stability

Thestability of an engineering material can be defined as the ability ofthe material to perform under various environmental conditions suchas fluctuating temperatures, radiation, among other conditions. Agood engineering should perform under various environmentalconditions (Mendesand Lago 2014).&nbsp

Fabricability

Fabricabilityof material is defined as the ability of the material that indicatesthe ease with which it can be fabricated during manufacturing. Itdefines the possibility and ease with an engineering material can befabricated into a desired shape or form to produce a givenengineering part or product. The ease with which a specificengineering material can be fabricated is a key consideration inmaterial selection for engineering applications (&quotEngineeringMaterials: Features &amp News on Composites, Coatings, Metals&quot,2016).

Design

Theselection of material for an engineering application is also dictatedby the product design. The design of an engineering part or productdetermines the ductility and strength required in the material beingchosen for the part or product. Therefore, the design of anengineering part should be done with a consideration of themechanical properties of the material candidates (Gere and Goodno2013).&nbsp

CorrosionResistance

Corrosionresistance is another important criterion in the engineeringselection. For instance, when an engineering product or part is to beused in industrial environment with the corrosive substance, thereare high chances that the material of the part or product will beeroded eventually. Therefore, such parts or products should be madeof materials that have high resistance to corrosion. Corrosion is anatural process that converts a refined material into an oxide. Itreduces the strength of an engineering gradually (Mendes and Lago2014).&nbsp

Cost

Tomanufacture an engineering part successfully, commercially, andprofitably, the total cost of production must be considered. Themarket price of an engineering product is dependent on severalfactors such as the material cost, material’s processing cost,labor cost, etc. Before an engineer settle for a certain engineeringmaterial, the cost of the material, processing cost and, the laborshould be considered with an intention of minimizing the totalproduction cost. The market price of a final engineering should becompetitive and reasonable (Ashby 2011).&nbsp

Thetable below shows four types of steel alloys with differentcompositions of Carbon, Manganese, Chromium, Nickel, Cobalt,Molybdenum, Tungsten, and Niobium. The types of alloys are to be usedin making cuttingtools, rail track points, cutlery or surgical instruments, and theturbine blades.

Alloy

Percentage of Alloying Elements

Carbon (C)

Manganese (Mn)

Chromium (Cr)

Nickel (Ni)

Cobalt (Co)

Molybdenum (Mo)

Tungsten (W)

Niobium (Nb)

1

1.5

4.6

5.0

12.5

2

0.08

16.2

11.5

1.5

1.0

3

0.8

18.0

9.0

4

1.0

13

TheEffects of the Key Alloying Elements

Fromthe table above, each steel grade has different key alloyingelements. The effects of the key alloying elements used in the foursteel grades are as discussed below.

Carbon(C)

Carbonis an essential element in alloy steels. Most of the steels areclassified based on the percentage of carbon in the alloy. Carbonelement is an austenite former, which enable it to increase themechanical strength of a steel alloy. In ferritic steel grades,carbon significantly reduces both corrosion resistance and toughness.In martensitic steel grades, carbon strongly increases mechanicalstrength and hardness but reduces toughness. Carbon element is addedto enhance mechanical hardness and strength. It reacts with ironparticles to form iron carbide.

Manganese(Mn)

Manganeseis added to enhance hot ductility. At low temperatures, manganeseacts as an austenite stabilizer, while at high temperatures, it is aferrite stabilizer. It also added to increase solid-solution hardnessand strength, as well to improve hardenability. However, it is poorin forming carbide. Moreover, manganese counteracts the brittlenessthat may be formed as a result of the reaction between iron andsulfur. The brittleness is due to the formation of iron sulfidelayer.

Chromium(Cr)

Chromiumis one of the important alloying element in steel work. Chromiumelement has excellent corrosion resistance. Therefore, the mainreason for adding chromium to steel is to increase corrosionresistance. All the stainless steel contain at least ten percent ofchromium. The higher the percentage of chromium in a steel alloy, thehigher the corrosion resistance. Also, chromium, being one thehardest metals, increases solid-solution hardness, strength, andhardenability. As a result, chromium increases the abrasion and wearresistance of a steel alloy (Ashby 2011).&nbsp

Nickel(Ni)

Nickelis an essential element in steel alloys. It is added mainly toincrease toughness and ductility. Also, it increases corrosionresistance of a steel alloy. Also, nickel increases solid-solutionhardness. However, nickel does not form carbide with carbon (Ashby2011).&nbsp

Cobalt(Co)

Cobaltis an important alloying element steel alloys. It is added to enhancehardness and strength. It also improves the alloy’s hot hardness.However, it decreases hardenability. Just like nickel, cobalt is alsoa poor carbide former (Herweck 2011).&nbsp

Molybdenum(Mo)

Molybdenumis an important element used in steel work. It is added mainly toenhance mechanical hardness and strength of a steel alloy. It is anexcellent carbide former. It is stronger than chromium in forming acarbide. It improves the alloy’s high-temperature characteristics,including creep strength. Also, it increases resistance to corrosion(Mendes and Lago 2014).&nbsp

Tungsten(W)

Tungstenis also one the most important alloying elements in steel. Due itshigh melting temperature, it is the best element for enhancinghigh-temperature properties of a steel alloy. Tungsten is anexcellent carbide former. The tungsten carbide forms a hard, abrasionresistant compound in a steel alloy. Therefore, tungsten increasesthe solid-solution hardness and strength in steels (McNaughton2015).&nbsp

Niobium(Nb)

Niobiumis an excellent carbide and ferrite former. It is added to improvethe resistance to corrosion. In ferritic grades, niobium is added toenhance toughness. However, in martensitic, an addition of niobiumreduces hardness and improves tempering resistance (McNaughton2015).&nbsp

MaterialSelection for Various Engineering Applications

Fromthe above discussion, the best material for the following engineeringapplications can be chosen as discussed below.

CuttingTools

Severalengineering materials can be used for manufacturing cutting tools. Acutting tool is required to possess certain basic properties toproduce high-quality parts. They include high hardness, high thermalconductivity, low coefficient of friction, high toughness, high wearresistance, high fabricability, high corrosion resistance, high hothardness temperature, and low cost (Galimberti and Swinehart 2011).The properties are as explained below.

Hardness.Themechanical strength and hardness of a cutting tool should bemaintained within a wide range of temperatures. A good cutting toolshould be between thirty and fifty percent harder than the work-piece(Galimberti and Swinehart 2011).

WearResistance.Wear resistance of a cutting is described as the ability of the toolattain an acceptable tool life before it is replaced. A good cuttingtoll should not fracture or break before its acceptable life span(Galimberti and Swinehart 2011).

Toughness.Toughness of a cutting tool is required so that the tool do notfracture or chip, especially during sporadic cutting operations.

Thecommon alloying elements used in the manufacturing of cutting toolsinclude Tungsten, Cobalt, Chromium, and Carbon. Each of theseelements adds certain specific properties to the cutting tool. Forinstance, Molybdenum increases hardness and wear resistance. Chromiumincreases the tool’s resistance to corrosion and abrasion. Thefunction of Cobalt in the tool material is to increase ductility,hence, increasing mechanical strength. The carbon element reacts withtungsten to form tungsten carbide, which increases high hardness andresistance to corrosion.

Consideringthe above requirements for a cutting tool, and from the materialcandidates given in the table, the Alloy 1 comes out to be the mostsuitable material for this application. In a cutting tool, theemphasis is put on the material’s hardness. The Alloy 1 has thehighest percentage of Tungsten, which makes it the hardest of thefour material candidates.

RailTrack Points

Themain requirements for the rail track points are high mechanicalhardness, strength, resistance to corrosion. The suitable materialcandidate for this application is Alloy 4. The alloy is a high carbonsteel, which makes it possess the desired hardness. Also, thepresence of manganese in the alloy gives it the required strength.Moreover, manganese increases ductility in the material, whichincreases its fabricability.

Cutleryand Surgical Instruments

Themajor consideration in the manufacture of cutlery and surgicalinstruments are mechanical hardness, toughness, corrosion resistance.Normally, the cutlery and surgical instruments are subjected toextreme environmental conditions, such as high moisture contents.Such conditions promote corrosion. Therefore, the material of thesematerials must possess high corrosion resistance. Also, since thecutlery and surgical instruments are required to retain sharpness forlong times, the material used for manufacturing them must have highmechanical strength and hardness (Ashby 2011).Thematerial candidate with these requirements is Alloy 3. The alloy hasa low carbon content, which makes it ductile, hence easy to machine.Also, the material has a high percentage of chromium. As discussedabove, the higher the percentage of chromium, the higher thecorrosion resistance. The high percentage of chromium increaseshardness. Moreover, the alloy has high nickel content, which improvesits toughness.

TurbineBlade

Inturbine blades, the key considerations include toughness, strength,and resistance to corrosion. Normally, turbine blades are used inextreme environmental conditions such as high moisture contents andhigh temperatures. Such conditions promote corrosion. Therefore, thematerial of the blade must have high resistance to corrosion. Also,the turbine blade should possess high mechanical strength towithstand the forces that it may be subjected during operation. Thebest material candidate for this application is Alloy 2. The highpercentage of chromium in the alloy gives it the desired corrosionresistance. The presence of nickel and niobium in the alloy gives tothe required toughness. Molybdenum enhances the alloy’s hardnessand increases the melting point since the turbine blades aresubjected high temperatures. The low carbon content introducescertain degree of ductility in the material. This makes it easier tomachine.

Conclusion

Materialselection is an important process in engineering, which is carriedout to choose the most suitable materials for specific engineeringapplications. It is performed to ensure that final products performas desired both commercially and industrially. Also, a propermaterial selection is performed to ensure that the product or partsells in the market. The market value of a product is normally adirect function of its production cost. Therefore, the lower theproduction cost, the lower the market price. Failure to selectmaterials carefully not only result in the low competitiveness of aproduct in the market, but also leads to its failure duringoperation. The choice of material for a particular engineeringapplication depends on the intended use of the final product. Forinstance, in engineering applications that require high mechanicaltensile strength, only the materials that possess high strengthshould be chosen. Cost is another important consideration inmaterials selection. Sometimes a designer is required to workbackward before they settle on a particular design of a product. Forinstance, the final cost of a material cost should be consideredbefore choosing a particular material.

ReferenceList

AdvancedEngineering Materials – Wiley Online Library.(2016).&nbspOnlinelibrary.wiley.com. Retrieved 29 November2016, fromhttp://onlinelibrary.wiley.com/journal/10.1002/(ISSN)1527-2648

Ashby,M. (2011).&nbspMaterials selection in mechanical design. 1stEd. Amsterdam: Butterworth-Heinemann.

Askeland,D. (2014).&nbspThe science and engineering of materials. 1stEd. Boston: PWS Pub.

Barrett,C., Nix, W. and Tetelman, A. (2013).&nbspThe principles ofengineering materials. 3rd Ed. [Englewood Cliffs,N.J.]: [Prentice-Hall].

Callister,W. (2012).&nbspMaterials science and engineering. 1stEd. New York: John Wiley &amp Sons.

EngineeringMaterials: Features &amp News on Composites, Coatings, Metals.(2016).&nbspMaterialsforengineering.co.uk. Retrieved 29November 2016, from http://www.materialsforengineering.co.uk/

Galimberti,J., and Swinehart, H. (2011).&nbspCutting tool materialselection. 1st Ed. Dearborn, Mich.: American Societyof Tool and Manufacturing Engineers.

Gere,J. and Goodno, B. (2013).&nbspMechanics of materials. 1stEd. Stamford, Conn.: Cengage Learning.

Herweck,D. (2011).&nbspMechanical engineering. 1st Ed.Mankato, MN: Compass Point Books.

McNaughton,K. (2015).&nbspMaterials engineering. 2nd Ed. NewYork: Chemical Engineering.

Mendes,G., and Lago, B. (2014).&nbspThe strength of materials. 1stEd. New York: Nova Science Publishers.