2Temperature Effects on Material Properties Temperature changes and extremes affect the value of many engineering propertiesyield, modulus, toughness, corrosion resistance, creep, relaxation, viscosity, shrinkage, solubility…..
5Thermal 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.
6Temperature vs. Expansion t is the coefficient of thermal expansion.t is typically a constant.
7Surface Properties Hardness Impact Energy Scratch hardness Surface HardnessImpact Energy
8Hardness - 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.
9Surface 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.
10Types 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°
11Use of hardness Surface hardness of heat treated metals Quality control of heat treatment processCorrelated with other propertiesYield strength“Brittleness”
12Impact tests Charpy V-notch - Measure energy required to rupture specimenIzod V-notch- Same as Charpy butdifferent specimen
13Use of impact resistance Quantify resistance to dynamic impacts and crack sensitivityQuantify the “transition temperature” of an alloy(ductile – brittle behavior)Impact Energy, JoulesTemperatureDuctileBrittle