Metallography and Microhardness

Question 1

metallography

Answer 1

the study of structural characteristics or constitution of a metal or an alloy in relation to its physical and mechanical properties

Question 2

metallography- ways to prepare a metal include

Answer 2

grinding, polishing, etching.

the reveal the microstructural constituents

Question 3

metallography consists of

Answer 3

macroscopy

microscopy

Question 4

macroscopy

Answer 4

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

Question 5

microcopy

Answer 5

study of prepared metal surfaces using high magnifications

Question 6

microscopy applications

Answer 6

microhardness testing

grain size measurement

study of the distribution of secondary phase

observation of non-metallic inclusions

locating cracks and defects in the specimen

Question 7

stages of preparation

Answer 7

sectioning
mounting
coarse grinding
fine grinding
rough polishing
fine polishing
etching

Question 8

sampling

Answer 8

required the selection of a specimen such that it is characteristic of the material and should fufill the object of examination

Question 9

mounting

Answer 9

metallographic samples are typically “mounted” in a phenolic, bakelite, or epoxy resin

Question 10

grinding

Answer 10

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

Question 11

rough polishing

Answer 11

remove surface deposits or level irregular surfaces and prepares them for further polishing…..

decreasing grit from 250-800

Question 12

fine polishing

Answer 12

grit with decreasing coarseness, make specimen scratch free, consists of pouring an abrasive suspension on cloth and rotating the wheel at a suitable speed

Question 13

commonly used abrasives are:

Answer 13

alumina
chromium oxide
diamond dust
magnesium oxide

Question 14

etching

Answer 14

after polishing, the microstructural constituents of the sample are revealed by using a suitable chemical or electrolytic etchant….. observe microstrucutre or grain size

Question 15

___ the specimen___ for every change in polishing stage in fine grinding

Answer 15

rotate 45

move the specimen in the opposite direction of rotation of the polishing wheel in rough and fine polishing

Question 16

microhardness

Answer 16

static indentations made with loads not exceeding 1 kgf…

indenter= vickers diamond pyramid or knoop

Question 17

microhardness typical applications

Answer 17

bulk hardness of small samples

evaluation of hardness of welds

hardness of thin coatings

testing very thin materials like foils

Question 18

pyramidal diamond indenter is impressed into the material at loads from

Answer 18

15-1000 gf

one indenter covers all the materials

Question 19

The Vickers hardness test uses a _____ with the shape squared based pyramid with a an angle of __ between opposite faces as the indenter

Answer 19

diamond indenter ….angle 136,,,,

Question 20

the main drawback of vickers test is need to

Answer 20

optically measure the indent

time consuming