MATS3001 “Typical” exam questions.

As discussed in a number of BB Collaborate sessions, the exam for MATS3001 will focus on
students demonstrating understanding of the course material. To that end, the questions in
the exam held on May 2nd will focus on students being able to analyse and interpret data,
perform calculations etc.

Questions will include a number of numerical questions as well as a number of (relatively)
short answer questions.

These questions can be discussed in the BB Collaborate sessions on April 27th and 29th.








1. The above data show a summary of incidences of the Portevin Le Chatelier (PLC)
effect for an experimental alloy tested over a range of strain rates and temperatures.
The PLC effect is identified to either not occur (no serrations) or occur (serrated
flow) and for each strain rate limits to the range of temperatures over which the PLC
effect occurs are given. Explain why no serration is seen to occur at room
temperature or (sub-zero) temperatures. Why does the range over which the PLC
effect is observed move to higher temperatures at the highest strain rate?


2. To what extent do refinements in grain size improve the mechanical properties of a
material?
























3. The above graph shows hardness versus concentration of alloying addition for
ferritic steels. Which element provides the most powerful strengthening per atomic
per cent of addition? Suggest reasons why the strengthening increment provided by
Mn is greater than that provided by Co. Suggest why the data for Nb and Ti is only
given for additions less than 1%, whereas data for additions of up to 5% Cr are given.












4. The above data shows a Larson-Miller plot for a high strength steel (3Cr-3WVTA) in
the normalized and tempered condition. (Assume C = 20). If components are to
operate under a stress of 40 MPa and 625°C, estimate the expected lifetime (in
months). What would be the maximum stress that a component could operate under
if it was designed to last for 10,000 hours at a temperature of 600°C?






















5. The above shows TEM images from an aluminium 7xxx alloy. Why in Figure (a) are
the largest particles located at the grain boundary? Many of the particles visible in
Figure (b) taken at higher magnification appear to be rod-shaped? Why would this
shape be desirable in achieving maximum strength for this alloy? Suppose this alloy
was heat treated at 300°C for 2 hours – what might happen to these rod shaped-
particles?




















6. The above figure shows the relationship between elongation and ageing time for a
6xxx alloy. Explain why elongation of the alloy drops rapidly at 200C in the first 10
hours of ageing.














7. The above figure shows Hall-Petch data for steels. Calculate the values of the Hall-
Petch parameter and s0 for the alloy tested at 293K (you will be required to show
any mathematical working). Estimate the strength of the material tested at 77K with
a grain size of 10 microns? Explain why the strength of the alloys, for a given grain
size, decreases with increasing test temperature.