An engineering research team investigates two types of steel: one produced by adding 1.2 mass % carbon (Sample X) and another produced by substituting 2.0 mass % nickel for iron atoms (Sample Y). Both samples are compared with identical, very pure iron reference bars.
The team measures hardness (in HV) and bulk electrical resistivity (in μΩcm) for each sample at 298 K with the following results:
Sample
Hardness (HV)
Resistivity (μΩcm)
Pure Fe
70
9.8
X
180
10.1
Y
120
10.9
Use the data and your knowledge of solid-state structure to answer the questions below.
(a) Describe the different lattice modifications present in Samples X and Y relative to pure iron.
(b) Using the particulate-level structural differences, justify the observed order of hardness among the three samples.
(c) Despite a larger increase in hardness, Sample X shows a smaller change in resistivity than Sample Y. Provide a mechanistic explanation for this observation.
(d) Propose one additional experimental test (other than hardness or resistivity) that could further distinguish the mechanical behavior of Samples X and Y. Briefly justify how the results would relate to their underlying lattice structures.