Prakt. Met. Sonderband 52 (2018) 255
NESE Qyank
ag As in every microstructural/stereological analysis, the first step is to obtain good-quality and
ag % representative micrographs. Given the small size that the carbides in PM tool steels might
Moye ot have, scanning electron microscopy (SEM) micrographs are employed.
Shaiig ey In the second step, the intensity information of each pixel and its surrounding is used to
Nhe ny N create a binary, i.e., black and white (B&W) version of the microstructure. This is achieved
ey Sch by a succession of several operations such as lighting enhancement, multi-level greyscale
fed andig thresholding, morphological opening and closing, distance transform and watershed.
ar “do Thirdly, perimeters and areas are measured from the B&W images.
ital 9 they Finally, these measurements are employed to compute the desired microstructural
5 "essa parameters.
gy An overview of the general scheme is presented in Figure 1.
0, the
3085 is sti pe
Yam =
N ole phase:
el a \ Size distribution
tive an Area measurements Shape
nd User ski Serimeter Contiguity
dss Sofware neasurements Abrasive Wear:
ation abo . Mean free path in the
developed wi matrix
Figure 1 — Implemented image processing and analysis scheme. All four steps are: a)
SEM original image, b) Phase recognition and binarization, ¢c) Measurements, d)
istance? Parameter computation.
's devel , Co
vith i This computations are possible thanks to the derivation of the next equations:
26 distribution }
Se A_1-v _QR, .
d PG TTC A
manufacturing v =
nd Whe . .
a, This set of equations compactly relate A, d and v with four descriptors of the hard phase: a
i. nthe rs size distribution parameter (Q), a shape parameter (R), a contiguity parameter (C) and a
ise EAN area descriptor (d,.).
ase
| 2.2. Relation between wear parameters and microstructural features
As studied by Zum Gahr [3], the loss of volume (%) per scratch length (s) in a single phase
material can be determined by introducing the f„„ parameter as well as the cross-sectional
area of the groove (4,):
V,
Is = Ay fap (3)
. Information on how to obtain the f,;,, parameter is not provided here to keep the article length
MESS t5 a minimum, but more details can be found in [3, 8].
To undercover the relation between wear parameters and microstructural features in the
micro-machining level, a simple mathematical model for the penetration depth was
| introduced. Assuming that the depth h, changes depending on the phase currently being
wets seratched, it is then possible to name h, the attained depth while scratching the matrix phase
and h, the measured depth in the carbide phase. Since d and A are linear density
1s N or parameters, we assumed that they completely describe the microstructure for the problem
he discuss
(2°
