MSCI 301 - Materials Science - Spring 2004


Mon. Jan 12: Aristotelian Elements, Nucleosynthesis

Fri. Jan 16: Bohr orbitals: 1s, 2s, 2p, 3d, also Effect of n & l quantum numbers, Hydrogen-like energy levels, Moseley's Law

Wed. Jan 21: sp3 hybrid orbitals

Fri. Jan 23: Number of elastic constants for each crystal system and Dependence of Material Properties on Crystal Direction .

Mon. Jan 26: Tetrahedral and octahedral interstitial sites in an FCC Bravais lattice. See also BCC case.

Fri. Jan 30: More interstials in FCC, HCP, BCC lattices. These came from GAMGI.ORG , tutorials.

Mon. Feb.2: Term paper assignment - topic and outline due Mon. Feb. 9.

Fri. Feb 6: Transmission electron microscope (TEM) photos of dislocation loops caused by shear strain acting on crystal defects. The loops tend to lie in certain crystallographic planes and the sides of each loop tend to lie along certain crystallographic directions. In each loop, one pair of opposite sides are edge-type and the other pair are screw-type. Also, see schematic drawings of three-dimensional coherent, semi-coherent & non-coherent precipitates in a crystal.

Mon. Feb.9: Comparison of the normal and lognormal distributions, both with standard deviation=1. See reading assignment on the subject of powder metallurgy.

Wed. Feb.11: Log-normal graph paper, for use with "censored" data. Also some clarification about the term paper, sent to everyone as an email on 2/10/04.

Fri. Feb.13: Here are two extra problems to be included in homework #5. You'll also need the graph paper from Wed.Feb.11. For self-diffusion in polycrystalline Ag, grain boundaries dominate below about 950 deg.K (note the relatively low activation energy and higher diffusivity) while lattice diffusion dominates above that temperature (note the relatively high activation energy and lower diffusivity). See plot. This type of behavior is common in nearly all polycrystalline materials. Free surface diffusion is faster and has even lower activation energy than grain boundary diffusion. See schematic diagram where the horizontal axis is normalized for various alloys by plotting melting temperature over ambient temperature.

Mon. Feb.16: A graph of the error function and some reference information about it.

Wed. Feb.18: Two more binary equilibrium phase diagrams: Fe-Ni diagram which is more complete than Figure 8.16 in the text and shows the magnetic transformation as well as formation of three compounds at low temperature ....also an Al-Cu diagram which includes thirteen stable crystal structures (intermetallic compounds) as well as six eutectoid, seven peritectoid and various other special points (with zero degrees of freedom).

Fri. Feb.27: See summary of scanned probe microscopy. All these instruments depend on piezoelectric actuators.

Fri. Mar.12: See hardness conversion tables, part 1 and part 2, from Wilson Instrument. These can be used to convert between hardness measurements of various types and also, for steel, to convert hardness readings into ultimate tensile strength. Note that the units for Knoop, Brinell and DPH (Vickers) hardness are all Kg per square mm, while the units for tensile strength are K psi. Rockwell hardness numbers don't have units. Two other useful references about hardness testing are from the Univ. of Maryland and from the Gordon England company.

Mon. Mar.15: Here's homework #8, including one one extra problem (not from the textbook) as well as a note concerning an error in the text, Table 5.2. Also, see examples of twinned crystals (mostly minerals) from Hammond and from Giacovazzo et al an "elbow" twin in tetragonal cassiterite (SnO2) with twin plane {101}.

Wed. Mar.17: You've seen the movie, now read the metallurgical failure analysis report about the RMS Titanic.

Mon. Mar.22: Graphs of stress intensity as a function of crack length for center cracked & single edge notched strips in tension as well as double edge notched strip in tension & single edge notched strip in bending. Also a graph showing the effect of specimen thickness on fracture toughness and a graph showing variation of Kic with temperature.

Wed. Mar.24: A chart from Ashby, Kic as a function of yield stress for a wide variety of solid materials. This is especially useful for comparing critical crack sizes among the various materials. Also a few photos of cracked Liberty ships from the bad old days before the development of fracture mechanics. A few more of these photos. A photo of the world's first model of jet airliner, the De Havilland Comet which was prone to sudden fracture of the fuselage and loss of the entire plane due to growth of cracks from rivet holes near windows and hatchways. See description.

Mon. Apr.5: The four types of cast iron, photomicrographs from Callister. Also a short presentation, "The First Aerospace Aluminum Alloy: The Wright Flyer Crankcase" by Frank Gayle of NIST.

Fri. Apr.9: To compare various properties of ceramics with those of metals (and other materials) see charts by Ashby: elastic modulus vs. density, strength vs. temperature, thermal expansion vs. thermal conductivity and , Kic vs. yield stress.

Mon. Apr.12: Another Ashby chart summarizing corrosion of materials in various chemical environments. Although not mentioned specifically, many ceramics can be severely affected by fluorides such as hydrofluoric acid.

Wed. Apr.14: Two items about amorphous (glassy) materials: TEM photos and article about metallic glass research from Todd Hufnagel at Johns Hopkins Univ. and an interesting article about fiberglass from the Rio Tinto Borax Company.

Fri. Apr.16: Potential-pH corrosion diagrams for Al and Pt from Pourbaix. These diagrams show the combinations of electrical potential and pH which result in corrosion (metal ions formed), passivation (various oxides or hydroxides formed) and immunity from corrosion (pure metal is stable).

Mon. Apr.19: In the late 1960's Gordon Moore at Fairchild Instrument noticed that the complexity of integrated circuit (IC) chips was doubling every year or so. This trend has persisted in the semiconductor industry for decades (see trend for Intel processors). Similar trends exists for other companies' memory and logic products, due in no small part to thousands of engineers working to understand the effects of electric currents, mechanical stress, temperature and impurities on various metals, insulators and semiconductors used in building those chips.

Resistivity r and temperature coefficient of resistivity a (or TCR) for forty pure elements are shown in a table from Pollock. The effects of various solute atoms on the resistivity of Au, Ag and Cu are tabulated here.

Wed. Apr.21: Besides IC chips, resistors have many other applications, including

1) Temperature measurement, using r (T) = r 0C (1 + a *T) per Smith eqn. 13.8 . Pt works well in this application.

2) Strain measurement: if one starts with the equation for resistance R = r l /A (Smith eqn. 13.2), then takes the total derivative D of both sides and divides the result by the original equation, the result is D R = (AD l - l D A)/ l A . Noting that, due to constant volume, strain e = D l /l = -D A/A (Smith eqn. 5.4) it can be shown that D R/R = 2e for "normal" metals. Here, D R is just the change in resistance due to strain. More generally, a materialís "gage factor" is defined as g = D R/Re . See values for various materials.

3) Phase diagram determination: Temperature coefficient of resistivity a and resistivity r depend on alloy composition as shown in a figure by Pollock.

4) Heat treatment of precipitation hardening alloys. - Maximum hardness, yield and tensile strength occur in precipitation-hardening alloys when the number of GP zones is greatest. At this same point electrical resistivity is also greatest. So, an electrical resistance method is used commercially to control heat treatments of such alloys, particularly aluminum alloys for aircraft. In many cases these are aged just past the peak-aged condition to improve corrosion resistance at the expense of a relatively small decrease in strength. This method is much quicker, easier and more accurate than hardness testing, electron microscopy, and other alternatives.