Metallography and Microhardness Flashcards
metallography
the study of structural characteristics or constitution of a metal or an alloy in relation to its physical and mechanical properties
metallography- ways to prepare a metal include
grinding, polishing, etching.
the reveal the microstructural constituents
metallography consists of
macroscopy
microscopy
macroscopy
study of metals either by the unaided eye or with aid of low powered microscope
reveals some of the important deals such as uniformity of structure, presence of defects ect
microcopy
study of prepared metal surfaces using high magnifications
microscopy applications
microhardness testing
grain size measurement
study of the distribution of secondary phase
observation of non-metallic inclusions
locating cracks and defects in the specimen
stages of preparation
sectioning mounting coarse grinding fine grinding rough polishing fine polishing etching
sampling
required the selection of a specimen such that it is characteristic of the material and should fufill the object of examination
mounting
metallographic samples are typically “mounted” in a phenolic, bakelite, or epoxy resin
grinding
removes epoxy layer and prepares specimen surface for further polishing. it removes sharp or jagged edges from side so they do not rip or grab the cloth
rough polishing
remove surface deposits or level irregular surfaces and prepares them for further polishing…..
decreasing grit from 250-800
fine polishing
grit with decreasing coarseness, make specimen scratch free, consists of pouring an abrasive suspension on cloth and rotating the wheel at a suitable speed
commonly used abrasives are:
alumina
chromium oxide
diamond dust
magnesium oxide
etching
after polishing, the microstructural constituents of the sample are revealed by using a suitable chemical or electrolytic etchant….. observe microstrucutre or grain size
___ the specimen___ for every change in polishing stage in fine grinding
rotate 45
move the specimen in the opposite direction of rotation of the polishing wheel in rough and fine polishing
microhardness
static indentations made with loads not exceeding 1 kgf…
indenter= vickers diamond pyramid or knoop
microhardness typical applications
bulk hardness of small samples
evaluation of hardness of welds
hardness of thin coatings
testing very thin materials like foils
pyramidal diamond indenter is impressed into the material at loads from
15-1000 gf
one indenter covers all the materials
The Vickers hardness test uses a _____ with the shape squared based pyramid with a an angle of __ between opposite faces as the indenter
diamond indenter ….angle 136,,,,
the main drawback of vickers test is need to
optically measure the indent
time consuming
