MEE1005 Materials Engineering and Technology L10

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DEVAPRAKASAM DEIVASAGAYAMProfessor of Mechanical Engineering

Room:11, LW, 2nd FloorSchool of Mechanical and Building Sciences

Email: devaprakasam.d@vit.ac.in, dr.devaprakasam@gmail.com

MEE1005: Materials Engineering and Technology (2:0:0:2)

Devaprakasam D, Email: devaprakasam.d@vit.ac.in, Ph: +91 9786553933

mailto:devaprakasam.d@vit.ac.in,

mailto:dr.devaprakasam@gmail.com

MEE1005 MATERIALS ENGINEERING AND TECHNOLOGY

Purpose of Engineering /Education/Research

There are two important purposes and driving force behind the Engineering/Education/Research:

1. Minimum consumption of Energy and Materials without sacrificing the efficiency and functionality.

2. Maximum conversion of Energy from one form to the other, to identify or design highly efficient process or system.

Purpose of Engineering /Education/Research

UNIT-I : Structure of Constitution of Alloys

Mechanism of Crystallization- Nucleation-Homogeneous andHeterogeneous Nucleation- Growth of crystals- Planargrowth – dendritic growth – Cooling curves - Diffusion -Construction of Phase diagram -Binary alloy phase diagram –Cu-Ni alloy; Cu-Zn alloy and Pb-Sn alloy; Iron-Iron carbidephase diagram – Invariant reactions – microstructuralchanges of hypo and hyper-eutectoid steel- TTT and CCTdiagram

When the solution above the transformation point is solid, rather than liquid, an analogous eutectoid transformation can occur. For instance, in the iron-carbon system, the austenite phase can undergo a eutectoid transformation to produce ferrite and cementite, often in lamellar structures such as pearlite and bainite.

Schematic representation of the formation of pearlite from austenite; direction of carbondiffusion indicated by arrows.

Photomicrograph of aeutectoid steel showing the pearlitemicrostructure consisting of alternatinglayers of α-ferrite (the light phase) andFe3C (thin layers most of which appeardark).

Consider a composition C0 to the left of the eutectoid, between 0.022 and 0.76 wt% C; this is termed a hypoeutectoid (less than eutectoid) alloy.

Schematic representations of the microstructures for an iron–carbon alloy of hypoeutectoid composition C0 (containing less than 0.76 wt% C) as it is cooled from within the austenite phase region to below the eutectoid temperature.

Schematic representations of the microstructures for an iron–carbon alloy of hypoeutectoid composition C0(containing less than 0.76 wt% C) as it is cooled from within the austenite phase region to below the eutectoid temperature.

Proeutectoid signifies is a phase that forms (on cooling) before the eutectoid austenite decomposes. It has a parallel with primary solids in that it is the first phase to solidify out of the austenite phase. Thus, if the steel is hypoeutectoid it will produce proeutectoidferrite and if it is hypereutectoid it will produce proeutectoid cementite.

Analogous transformations and microstructures result for hypereutectoid alloys, those containing between 0.76 and 2.14 wt% C, which are cooled from temperatures within the phase field.

Schematic representations of the microstructures for an iron–carbon alloy of hypereutectoid composition C1 (containing between 0.76 and 2.14 wt% C), as it is cooled from within the austenite phase region to below the eutectoid temperature.