In this research paper authors
performed various heat treatments to as-deposited sheet in order to study effects
of it on its microstructure and mechanical properties like strength and ductility.
For the strengthening of it, author used electron beam physical vapour deposition
(EB-PVD) by dispersion of Y2O3. In addition to that he used
various techniques like Fractography, cross section of micrograph, DTA
curve, Surface morphologies and XRD patterns.
For EB-PVD, author used L5
type equipment to do deposition of Cr, Al, O, Y, Ni. author considered stainless
steel as substrate on which evaporation will take place. Evaporation vapour sources
are one Y2O3 ingot with two Ni-20Cr-1.4Al ingot placed inside water
cooled crucibles. The evaporation process took place in the vacuum with
pressure less than 10-2 Pa. After that as-deposited sample treated
at 3 different temperatures and time durations.
Firstly as-deposited sample considered as T1 sample. author kept that
as-deposited sheet at 800 ? C for 3 hours refereed that sample as T2. Author performed
two more heat treatments by keeping first at 1100 ? C for 0.5 hours and 800 ? C
for 16 hours marked that sample as T3
and second at 1100 ? C for 3 hours refereed that sample as T4.
After every heat treatment
microstructure study performed by using different techniques like Differential
thermal Analyser (DTA), X-ray diffraction (XRD), X-ray Fluorescence spectrometry
(XRF) and scanning electron microscopy (SEM).
There were formation of equiaxed grain near the substrate and columnar grain as
it move away from substrate. Author provided explanations for formation of equiaxed
grain formation at substrate side and columnar grain formation away from substrate
side. Main reason to do heat treatment is because of micropores due to shadowing
effect present in the columnar grain. Micropores are responsible for the crack propagation
and affects mechanical properties of sheet. Author conducted the heat treatment
from 800 ? C to 1100 ? C. Author provided DTA graphical clarification for use
of temperature range as it has stable thermal stability over that temperature range.
From surface Morphologies of sample
T1, T2, T3 and T4, in sample T2 sintering
of columnar grains were occurred and new boundaries are formed. But still columnar
grains are present in the microstructure of sample T2. In sample T3 and T4 there
were very much grain sintering and boundary formation. Author provided the XRD
graph and provides various component in four samples. In T1 sample as author
mentioned that presence of ?-Ni and Y2O3 but there is no
symbolic representation of ?-Ni in T1
sample diagram. Also author discussed about diffraction peaks of Cr and Cr7Ni3
however there is no symbolic representation of Cr in Diffraction peaks in sample
T1. Also in case XRD graph of T2 sample there is no graphical representation of
Cr23C6 and author mentioned the presence of Cr23C6 in T3 sample. In
sample 4 there is formation of Y3Al5O12 which
consumes Y2O3. Because
of formation of YAG strengthening effect reduced.
Also from stress and
strain curve it shows that sample T2 has ultimate strength up to 1200 MPa after
that strength reduces to 960 MPa and 930
MPa in sample T3 and T4 respectively. T2 sample still have columnar grain structure
and there is no consumption of Y2O3.