2 Temperature Effects on Material Properties Temperature changes and extremes affect the value of many engineering propertiesyield, modulus, toughness, corrosion resistance, creep, relaxation, viscosity, shrinkage, solubility…..
5 Thermal ExpansionElevated Temperatures excite the electrons at the atomic level of any materialThe excited atoms can more easily move to a lower energy state and change orientation of atomic planesThis leads to dimensional changes in most materialsThere are exceptions, e.g. InVar, Ni-Cr alloy with a very low energy state that is not easily altered.
6 Temperature vs. Expansion t is the coefficient of thermal expansion.t is typically a constant.
7 Surface Properties Hardness Impact Energy Scratch hardness Surface HardnessImpact Energy
8 Hardness - Moh’s ScaleMoh scale is a surface scratch resistant scale based on minerals1 - Talc2 - Gypsum3 - Calcite (CaCO3)4 - Flourite5 - Apatite6 - Orthoclase (Feldspar)7 - Quartz8 - Topaz9 - Corundum (or sapphire)10 - DiamondThe Moh scale is a test of scratch resistance, based on empirical relationships developed in mineralogy.
9 Surface HardnessSurface hardness is quantified by determining the energy necessary to cause localized plastic deformation.A specific energy is imparted on a surface of a material and the amount of plastic deformation is quantified in most hardness procedures.Based on theory of plasticity.
10 Types of hardness tests Brinell ball original hardness testRockwell , rounded cone most common, (ASTM E18)Hardness values depends on: Method used, Shape of indenter - spherical, pyramidal, diamond shape, etc., Dimensions of indenter, Magnitude of load placed on indenterHowever, the hardness energy can be converted from one method to another.Vickers pyramid, first micro-hardness test, similar to Brinell, used for thin specimensKnoop diamond pyramid more refined micro-hardnessNote: P = Applied load in all tests120°
11 Use of hardness Surface hardness of heat treated metals Quality control of heat treatment processCorrelated with other propertiesYield strength“Brittleness”
12 Impact tests Charpy V-notch - Measure energy required to rupture specimenIzod V-notch- Same as Charpy butdifferent specimen
13 Use of impact resistance Quantify resistance to dynamic impacts and crack sensitivityQuantify the “transition temperature” of an alloy(ductile – brittle behavior)Impact Energy, JoulesTemperatureDuctileBrittle