22.08.2015   Comprehensive nuclear materials

Hardness

Typical room-temperature mechanical properties are summarized in Table 3. Measurements of micro­indentation hardness of ZrCx are prevalent in the literature. Hardness as a function of temperature is plotted in Figure 23 and as a function of the C/Zr ratio at room temperature in Figure 24. Room- temperature hardness ranges from 20 to 34 GPa (^2000-3300kgfmm~2). Hardness decreases with increasing test temperature, dropping to approxi­mately 0.5 GPa (49kgfmm~2) at 1800 K. Room — temperature hardness decreases with decreasing C/Zr ratio. Scatter in room-temperature measure­ments may be due to the variety of procedures reported (Knoop or Vickers indenter, 50-500 g load), which may not be in accordance with standard test methods.109,110 Hardness may be affected by sample microstructure, including porosity, grain morphology, and secondary phases. Residual stresses present in ion-beam deposited or pyrolytic ZrC coatings53,107 tend to inflate hardness, while free carbon reduces hardness.107,111

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450

2.13.5.3 Strength and 26, respectively. Only one room-temperature

tensile strength is reported,95 and ample scatter is

Ultimate tensile strength and bend strength are

evident in room-temperature bend strength. As in

Table 3 Room temperature mechanical properties of ZrCx

Ultimate tensile strength (MPa)

105

a

Bend strength (MPa)

100-300

b, c,d, e,f

Compressive strength (MPa)

345

c

834

a

Hardness (GPa)

20-34

a, c,d, g,h, i,j, k,l, m,

n, o,p, q,r, s

Fracture toughness, KIC

1.1

t

(MPam1/2)

2.8

u

aKosolapova.95

bShaffer and Hasselman.54

cLepie.96

dGridneva et a/.97

eFedotov and Yanchur.98

fLanin et a/.99

9Neshpor eta/53

hRamqvist.8

‘Funke et a/.100

jKohlstedt.101

kSamsonov et a/.102

‘Samsonov et a/.10

mArtamonov and Bovkun.103

nAndrievskii et a/.104

oVahldiek & Mersol.105

pTkachenko et a/.106

qKumashiro et a/.123

rKumashiro et a/.124

sHe et a/.107

tWarren.90

uLanin et a/.108

covalent ceramics, ZrC fractures in an exclusively brittle manner below ^1000 K,3 by both transgranular and intergranular means. Both tensile and bend strength increase with temperature as plastic slip in­creases the resistance to brittle fracture. A maximum precedes a subsequent decrease in strength, due to decreasing yield strength with temperature, and fail­ure occurs by macroscopic plastic deformation.

The effects of porosity, grain size, specimen sur­face condition, and impurity phases remain unex­plored, with sample preparation and microstructural characteristics tending to overshadow the effects of C/Zr ratio on strength. More measurements on well — characterized samples according to standard test methods are necessary.