ME 250

• line constructed when calculating phase
• compositions

involves one liquid and two solids

involves a single phase and two phase solid

(ϒ) FCC

(α) BCC

(Fe3C) Metal carbide, ceramic

BCT

(α+Fe3C) lamellar structure

(α+Fe3C) carbide plates

• α needles with C buildup in
• ϒ

When left at elevated temperatures for extended amounts of time the lamellar pearlite begins to form globs, and as time continues, the particles will get larger

sharing of valence electrons across the entire molecule

sharing of valence electrons in a localized region

Loss of material from a surface by the gouging-out of channels by hard particles lying etween the two surfaces being sheared past one another

Closely related to the primary cause of friction; invloves the transfer of material from one surface to another when the surfaces are being sheared past one another while a force is being applied normal to the interface. It is caused by cold welding across the touching asperities on the respective surfaces. The normal force acts to flatten the asperities and to increase the contact area over which cold welding can occur.

This occurs when a solid or semi-solid material lies in an interface and reduces the resistance to shear between the interfaces.

Same as boundary lubrication but at high velocities that gives it a much lower coefficient of friction.

The capacity of a steel to be transformed to martensite, instead of the diffusion-controlled transformed products, ferrite and cementite.

The hardening of the outside surfaces of a steel component by introducing extra amounts of carbon and/or nitrogen by diffusion at an elevated temperature, either to cause high-carbon martensite to form upon quenching, or to form a fine dispersion of alloy nitrides, and thereby to make the surface harder and more resistant to wear.

This is a surface hardening, or case hardening, treatment carried out by heating a steel in an atmosphere of H2/CH4 or CO/CO2, that deposits carbon on the surface. Inward diffusion of carbon raises the carbon content of the surface regions so that high-carbon martensite is formed when the steel is quenched.

Heating a cold-worked metal to remove the effects of strain hardening. It comprises the processes of recovery, recrystallization, and grain growth.

The heat treatment of steel that has been austenitized and quenched to form martensite. It involves heating in the ferrite + carbide region of the phase diagram (below the eutectoid temperature) to promote the decomposition of the metastable martensite. Done to improve toughness at the sacrifice of hardness.

Measure of the resistance of a material to the propagation of a crack when stress is applied

Usually means the resistance of a material to plastic deformation

A mechanism of hardening that involves the formation of a finely dispersed array of very small particles of a second phase that act as a strong barrier to dislocation motion. The alloy is solution treated and quenched, then aged at a temperature in the two-phase region.

The nucleation of a second phase in a supersaturated parent phase at random locations throughout the parent phase, without regard for the presence of any structural defects that could enhance the nucleation rate.

The nucleation of a second phase in a supersaturated parent phase not randomly, but on structural defects that act to lower the energy barrier for this nucleation, often by providing an existing interphace on which the new phase can form. Much less undercooling is required.

The amount of disorder in a system.

H, the sum of the internal energy, E, and the energy due to the pressure times the volume.

the energy that must be supplied to a system in metastable equilibrium to allow it to pass to a state of lower energy.

the ability of a material to deform plastically without fracturing

the maximum nominal stress a material can sustain.

In a Bcc, the site that produces the minimum overall strain energy in the lattice.

failure due to a dynamic and fluctuating stress in a structure.

A value of stress below which a material will not fail due to fatigue and where, theoretically, a material can endure infinite cycles.

participating elements

Majority element

minority element

physically and chemically distinct region of material

solid solution, single phase (syrup)

more than one phase (syrup + sugar)

Max concentration for which only a single phase solution occurs

A technique of joining two solid pieces by melting a filler metal and letting it flow into the crevice between the two pieces. Can occur at temperatures above 450 C.

A technique of joining two solid pieces by melting a filler metal and letting it flow into the crevice between the two pieces. Can occur at temperatures below 450 C.

The measure of a liquid on a solid surface to determine how well a liquid "wets" a surface. Depends on the energies of the interactions of the phases.

A process that involves the melting of a metal or alloy and pouring the molten metal into a mold in which it solidifies, taking the shape of the mold.