A researcher prepares a series of nitrogen-containing iron alloys by plasma nitriding
CHEMISTRY · Multi-part · AP · Chemistry · Compound Structure and Properties · Compound Structure and Properties
Problem
A researcher prepares a series of nitrogen-containing iron alloys by plasma nitriding. The measured lattice parameter of body-centered cubic iron and the corresponding ultimate tensile strength (UTS) for each alloy are listed below.
Alloy
Atomic % N
Lattice parameter / Å
UTS / MPa
I
0.00
2.866
280
II
0.20
2.870
420
III
0.50
2.879
610
Use the data to analyze structure–property relationships in these alloys.
(a) Calculate the percent increase in lattice parameter for Alloy III relative to pure iron (Alloy I). Show your work using appropriate significant figures.
(b) The researcher initially hypothesizes that the increase in UTS is directly proportional to the volumetric lattice expansion caused by nitrogen. Evaluate this hypothesis using the data provided. Include quantitative reasoning in your answer.
(c) Using concepts of lattice strain and packing efficiency, construct a mechanistic argument that connects the presence of interstitial nitrogen to the trend in tensile strength across the three alloys.
(d) Predict how the tensile strength and ductility are likely to change if the nitrogen content were increased beyond 0.50 atomic %. Provide two distinct structural reasons to support your prediction.