What influence does grain size have on mechanical properties of metal?

Answer 1

Influence of grain size on following properties of meatals:-

Hardness

Strength

Impactness

Toughness

Creep

Fatigue

Ductility

Malleability

Durability

Brittleness

INTRODUCTION

Yttria-stabilized tetragonal zirconia polycrystals

(Y-TZP) have proved to be important structural ceramics.

High strength and fracture toughness make them

attractive candidates for a number of demanding applications.

It was established that these advantageous

properties are strongly influenced by the ceramic microstructure

[1]. The relationships between microstructure

and mechanical properties in Y-TZP ceramics have been

studied extensively over the past two decades. It is now

generally agreed that the transformation toughening

effect (stress-induced tetragonal to monoclinic phase

transformation) in Y-TZP ceramics is grain size dependent

[2 7]. The larger the tetragonal grains the greater

propensity to undergo stress-induced transformation to

an equilibrium structure, resulting in an enhanced

toughness. The maximum toughness lies near the critical

grain size, where the tetragonal grains undergo

spontaneous tetragonal to monoclinic transformation

[7]. It was found that this critical grain size depends on

the yttria content [6, 7]. However, the critical grain size,

cited for 3Y-TZP (3 mol% Y2O3), which is the most

common zirconia ceramic material, varies significantly

(from 1 to 6 µm) [3, 8-9]. This could be attributed to different

processing procedures that result in different

ceramic microstructures. Thus, microstructural parameters

like porosity, grain size distribution, yttrium distribution

in grains, purity, phase assemblage, etc. need to

be taken into account for evaluating the microstructure.

In contrast to the fracture toughness the strength of

3Y-TZP reaches its maximum usually at smaller grain

size [5, 10]. Increasing size of failure origin coupled

with microstructural coarsening was identified as the

reason for strength decrease in ceramics with large

grains [11]. However, the increase of strength with

decreasing grain size cannot be extended to the

nanocrystalline range in 3Y-TZP. Eichler et al. [10]

determined the strength maximum for 3Y-TZP in the

submicron range and noted a clear strength decrease in

the nanocrystalline grain size range (~100 nm). In this

case, the strength decrease was attributed to the grain

size dependence of fracture toughness. A decrease in the

fracture toughness was observed as the grain size

changed from the submicrometre to the nanometre

range [10, 12]. These results validate the assumption

that the increase of critical defects during microstructural

coarsening is connected with the formation of

stress induced transformed regions at the free surface

and takes place preferentially in ceramics with grains

near the critical size [11]. Nevertheless, special processing

of TZP ceramics has been reported, which can partially

eliminate the increase of critical defects during

coarsening, resulting in almost constant strength, independent

of grain size [8, 9].

Original papers

Ceramics − Silikáty 52 (3) 165-171 (2008) 165

EFFECT OF GRAIN SIZE ON MECHANICAL PROPERTIES

OF 3Y-TZP CERAMICS

MARTIN TRUNEC

Department of Ceramics and Polymers, Brno University of Technology

Technicka 2896/2, 616 69 Brno, Czech Republic

E-mail: trunec@fme.vutbr.cz

Submitted June 21, accepted September 4, 2008

Keywords: Zirconia, Nanoceramics, Transformation toughening, Microstructure, Mechanical properties

The dependence of mechanical properties of 3Y-TZP ceramics on their grain sizes in the range from 0.19 µm to 2.15 µm has

been investigated. Vickers indentation tests were used to determine hardness and fracture toughness. The hardness decreased

with increasing grain size. The fracture toughness was almost constant for ceramics with the grain size up to 0.40 µm and

then grew with increasing grain size up to 7.8 MPam0.5 for ceramics with grain size of 1.8 µm. Above this grain size a spontaneous

transformation from tetragonal to monoclinic phase occurred. Ceramic samples with grain sizes of 0.30 µm and

0.78 µm yielded similar bending strength, 1020 and 1011 MPa, respectively. The microstructural coarsening required for

achieving larger grain size resulted in a higher scatter of strength values, which was demonstrated by a lower Weibull

modulus (13.0 vs. 7.54). The mechanical properties of nanocrystalline 3Y-zirconia ceramics coarsened to the grain size range

from 0.085 to 0.70 µm were also investigated and compared. Differences in mechanical behaviour of investigated ceramics

were observed and their possible causes discussed.

The objective of the present investigation was to

describe the dependence of mechanical properties of

commercial submicrometre-grained 3Y-TZP ceramics

on grain size and to compare their mechanical properties

to the mechanical properties of nanocrystalline zirconia

ceramics and nanocrystalline ceramics coarsened

to the submicrometre range.

EXPERIMENTAL

Two zirconia powders stabilized by 3 mol% Y2O3

were used for the preparation of test specimens. Commercial

zirconia powder TZ-3YB (Tosoh, Japan) was

cold isostatically pressed at 300 MPa into disk-shaped

bodies (diameter 28 mm; thickness 5 mm). For comparison,

a nanocrystalline zirconia powder B261 (BUT,

Czech Republic) was used. Details of the preparation of

the nanopowder can be found in [13]. Nanocrystalline

powder was cold isostatically pressed at 1000 MPa

without additives. The pressed bodies were 18 mm in

diameter and 5 mm thick. These bodies were ground to

a thickness of 1.5 mm prior to sintering. Both types of

bodies were densified by pressureless sintering in air at

temperatures from 1100 to 1650°C and dwell times

ranging from 0 to 50 hours.

The density of sintered specimens was determined

by the Archimedes method [14] with distilled water as

the immersing medium. The relative density of all ceramic

bodies was calculated using the value 6.1 g·cm-3 for

the theoretical density of 3Y-TZP. The grain size of the

sintered ceramics was evaluated by linear intercept

method (without correction) on scanning electron

microscopy (SEM) micrographs of polished and thermally

etched samples, in a similar way as in [15]. At

least three micrographs and total of 300 intersects were

evaluated to determine the average grain size for each

sintering batch. The phase composition of the sintered

ceramics was determined by X-ray diffraction (XRD)

analysis (X´pert, Philips, the Netherlands). The X-ray

spectra of polished and fracture surface were obtained

and the phase content was quantified using Rietveld

analysis.

For hardness and fracture toughness evaluation

Vickers indentation tests (LV 700, Leco, USA) were

used. Prior to indentation ceramic disks were mounted

in a resin and their surfaces ground and polished

(finishing with 1 µm diamond polishing fluid). Hardness

tests were performed at a load of 9.8 N (1 kg) and

a hold of 15 s. For determining the Vickers hardness,

HV (MPa), the following expression was used:

HV = 1.8544 P/d 2, (1)

where P is the applied load and d is the average diagonal

line length of the indentation. Ten indentations were

made for each sample. Toughness was calculated directly

from the crack lengths produced by Vickers indentation

at higher loads. Applied loads were 49.05 N (5 kg),

98.1 N (10 kg), 196.2 N (20 kg) and 294.3 N (30 kg)

always with a hold of 15 s. The crack lengths were

measured immediately after indentation using a calibrated

optical microscope. The fracture toughness,

KIc (MPam0.5), was calculated using the equation given

by Niihara et al. [16] for Palmqvist cracks:

KIc = 9.052 × 10-3 H3/5 E2/5 d c-1/2 , (2)

where H is the hardness, E the Young modulus (a value

of 210 GPa has been assumed for all the samples), d is

the average diagonal line length of the indentation and

c is the length of the Palmqvist crack. Ten valid measurements

were determined for each sample. The valid

measurements had to satisfy the requirements of the JIS

R 1607 [17] on acceptable indentation cracks.

The flexural strength was determined for selected

ceramic samples in four-point bending at a crosshead

speed of 2 mm/min, using fully articulated fixture with

a 10 mm inner and 20 mm outer span (in the "A" arrangement

according to the EN 843-1 [18]). Ceramic bars

with dimensions ca. 2.5 × 2 × 25 mm3 were cut from the

disks, ground and polished (finally with 1-2 µm grained

diamond paste). The parameters of the Weibull strength

distribution were calculated numerically, in compliance

with the ENV 843-5 [19].

RESULTS AND DISCUSSION

Microstructure and phase analysis

Various sintering schedules were applied to zirconia

green bodies to obtain dense sintered ceramics with

different grain sizes. Only those sintering schedules that

resulted in sintered densities exceeding 99% of theoretical

density (% t.d.) were employed.

A temperature of 1400°C was the lowest temperature

used in sintering the TZ-3YB ceramics; this was

necessary to obtain a dense sintered body. Larger grains

were obtained by the action of both higher sintering

temperatures and longer sintering times. Sintering schedules

and resulting densities and grain sizes are shown

in Table 1. The density of sintered TZ-3YB bodies

was constant up to the sintering temperature of 1650°C.

At the sintering temperature of 1650°C the density of

TZ-3YB ceramics decreased with increasing sintering

time. The structure of ceramics remained dense but the

theoretical density of these ceramics decreased due to

spontaneous transformation of the tetragonal into the

monoclinic phase (see Table 1). The average grain size

of TZ-3YB ceramics ranged from 0.19 µm (sintered at

1400°C/2 h) to 2.15 µm (sintered at 1650°C/50 h). The

Trunec M.

166 Ceramics − Silikáty 52 (3) 165-171 (2008)

critical grain size for spontaneous transformation from

tetragonal to monoclinic phase lies between 1.8 and

2.15 µm, where the content of monoclinic phase in TZ

3YB ceramics increased dramatically. The sample sintered

at 1650°C for 50 hours consisted of 77 % monoclinic

phase and was severely cracked due to volume

changes accompanying t→m transformation. Mechanical

properties could not be determined for these ceramics.

Several authors [8, 9, 11] have found large cubic

grains in thermally treated 3Y-TZP samples. In our case

no exaggerated grain growth was observed during the

microstructural coarsening.

The zirconia nanopowder B261 could be sintered

to dense bulk ceramics already at the temperature of

1100°C and dwell time of 4 hours. The microstructure

remained nanoscaled with an average grain size of

85 nm. Microstructural coarsening occurred at higher

sintering temperatures. However, the grain growth

kinetics of B261 ceramics was different from that in TZ

3YB ceramics. B261 ceramics sintered at 1550°C/5 h

had larger grains than TZ 3YB ceramics sintered under

the same conditions (0.70 vs. 0.48 µm). Moreover, the

density of B261 ceramics decreased sharply already at

small grain sizes where no monoclinic phase was

detected. Figure 1 shows the density as a function of

grain size for both TZ-3YB and B261 ceramics. The

reason for the density change in B261 ceramics is not

completely clear. According to the equilibrium phase

diagram given by Scott [20] the maximum amount of

cubic phase occurring in 3 mol% Y2O3-ZrO2 ceramics

sintered at 1550°C can be about 28 %. Matsui et al. [21]

showed that in tetragonal zirconia ceramics similar to

TZ-3YB the Y3+ ions segregated at grain boundaries

over a width of ~10 nm. Consequently, the cubic phase

started to form from grain boundaries and a triple junction,

at which Y3+ ions were segregated. A mixed tetragonal-

cubic structure was confirmed in TZ-3YB ceramics

by XRD analysis. In B261 ceramics the nanocrystalline

structure probably allowed other mechanisms of

phase structure development to take place that resulted

in the one-phase tetragonal structure. This fact could

explain the faster grain growth found in B261 ceramics.

Typical microstructures of TZ-3YB ceramics are shown

in Figures 2-4 and microstructures of B261 ceramics are

shown in Figures 5 and 6. The holes and voids visible in

micrographs on Figures 4 and 6 are believed not to be

pores but rather to result from pulling out the grains

during grinding and polishing.

Effect of grain size on mechanical properties of 3Y-TZP ceramics

Ceramics − Silikáty 52 (3) 165-171 (2008) 167

Table 1. Sintering schedules of zirconia ceramics and resulting density, grain size and monoclinic phase content.

Sintering schedule Density Relative density Grain size m - ZrO2

Powder/Sample (°C)/(h) (g/cm3) (% t.d.) (µm) (%)

TZ - 3YB 1400/2 6.07 99.5 0.19 0

TZ - 3YB 1500/2 6.08 99.7 0.30 0

TZ - 3YB 1550/0 6.09 99.8 0.29 0

TZ - 3YB 1550/2 6.09 99.8 0.40 0

TZ - 3YB 1550/5 6.09 99.8 0.48 0

TZ - 3YB 1550/10 6.09 99.8 0.54 0

TZ - 3YB 1600/2 6.09 99.8 0.53 0

TZ - 3YB 1600/5 6.09 99.8 0.68 0

TZ - 3YB 1600/10 6.08 99.7 0.78 0

TZ - 3YB 1650/10 6.08 99.6 0.99 3

TZ - 3YB 1650/20 6.08 99.6 1.37 6

TZ - 3YB 1650/30 6.04 99.1 1.79 13

TZ - 3YB 1650/50 5.68 93.1 2.15 77

B 261 1100/4 6.07 99.4 0.085 0

B 261 1300/6 6.04 99.0 0.19 0

B 261 1450/2 5.93 97.3 0.33 0

B 261 1550/5 5.71 93.6 0.70 0

Figure 1. Density of TZ-3YB and B261 ceramics as a function

of grain size.

Grain size (µm)

Density (g cm-3)

5.9

5.7

0.0

6.1

0.4 1.6 2.0

6.0

5.8

6.2

1.2 0.8

TZ-3YB

B261

Mechanical properties

Ten Vickers hardness tests were performed for each

ceramic. Average hardness values and their standard

deviation are given in Table 2. The hardness of TZ-3YB

ceramics clearly decreased with increasing grain size

from HV = 12620 MPa at grain size of 0.19 µm to

HV = 10971 MPa at grain size of 1.79 µm. The graph in

Figure 7 shows the hardness of TZ-3YB ceramics as a

function of the inverse square root of grain size. The

values in the graph could be reasonably fitted with a line

(r2 = 0.94), which means that this dependence followed

the Hall-Petch relationship. The hardness of B261

ceramics showed a higher dispersion but the linear fit

seems to be also reasonable. Different parameters of the

fits (lower hardness of B261 compared with TZ-3YB

ceramics) could be attributed to different phase structure

(mixed tetragonal-cubic vs. pure tetragonal).

Trunec M.

168 Ceramics − Silikáty 52 (3) 165-171 (2008)

Figure 2. SEM micrograph showing the microstructure of the

TZ-3YB ceramics sintered at 1400°C for 2 h.

Figure 3. SEM micrograph showing the microstructure of the

TZ-3YB ceramics sintered at 1650°C for 20 h.

1 µm

5 µm

Figure 4. SEM micrograph showing the microstructure of the

TZ-3YB ceramics sintered at 1650°C for 50 h.

Figure 5. SEM micrograph showing the microstructure of the

B261 ceramics sintered at 1100°C for 4 h.

5 µm

500 nm

Figure 6. SEM micrograph showing the microstructure of the

B261 ceramics sintered at 1550°C for 5 h.

2 µm

Different loads of Vickers indenter in the range

from 49.05 N (5 kg) to 294.3 N (30 kg) were used to

generate cracks in ceramic samples. It was verified

that in all cases only Palmqvist cracks were produced.

Fracture toughness values calculated from crack lengths

using Equation (2) at different loads are shown in

Table 2. The indenter load of 49.05 N (5 kg) generated

unstable cracks that grew further after load release. It

was not possible to measure the crack length reliably,

therefore the fracture toughness calculated from this

load was not included in the Table 2. The graph in

Figure 8 shows the dependence of fracture toughness of

TZ-3YB ceramics at different loads on grain size. The

values of fracture toughness determined at different

loads varied significantly. Nevertheless, the dependence

of toughness on grain size showed the same trend for all

loads. To obtain the most reliable value for the fracture

toughness, an average of values determined at different

loads was calculated (see Table 2). Figure 9 gives the

dependence of the average fracture toughness on grain

size for both TZ-3YB and B261 ceramics. This dependence

can be divided in two areas. The toughness was

almost constant (~ 5.1 MPam0.5) up to a grain size of

0.4 µm. In ceramics with larger grains, the toughness

increased linearly up to the grain size of 1.8 µm, where

the maximum toughness (7.8 MPam0.5) was found.

Above this grain size spontaneous transformation to the

monoclinic phase occurred. Figure 9 shows that both

ceramics, TZ-3YB and B261, followed the same toughness

dependence on grain size. It also follows from this

figure that the transformation toughness effect is grain

size dependent only above a particular tetragonal grain

size (approx. 0.4 µm).

Effect of grain size on mechanical properties of 3Y-TZP ceramics

Ceramics − Silikáty 52 (3) 165-171 (2008) 169

Table 2. Hardness, HV, fracture toughness, KIc, and their standard deviations, s, of zirconia ceramics.

Fracture toughness

Sintering Hardness 10 kg 20 kg 30 kg Average

schedule HV s KIc s KIc s KIc s KIc

Sample (°C)/(h) (MPa) (MPam0.5)

TZ - 3YB 1400/2 12620 186 4.94 0.07 5.29 0.06 5.49 0.05 5.24

TZ - 3YB 1500/2 12264 135 4.91 0.06 5.20 0.08 5.41 0.05 5.17

TZ - 3YB 1550/0 12137 224 4.89 0.29 5.10 0.06 5.38 0.05 5.12

TZ - 3YB 1550/2 12007 103 4.89 0.05 5.14 0.03 5.40 0.03 5.14

TZ - 3YB 1550/5 11970 113 5.06 0.07 5.23 0.05 5.45 0.06 5.25

TZ - 3YB 1550/10 11738 127 5.53 0.13 5.41 0.07 5.62 0.07 5.52

TZ - 3YB 1600/2 11858 363 5.15 0.16 5.29 0.07 5.57 0.04 5.34

TZ - 3YB 1600/5 11849 551 5.80 0.21 5.43 0.05 5.62 0.04 5.62

TZ - 3YB 1600/10 11588 176 6.39 0.09 5.53 0.03 5.72 0.03 5.88

TZ - 3YB 1650/10 11361 293 6.75 0.21 5.82 0.12 5.87 0.06 6.15

TZ - 3YB 1650/20 11145 341 7.11 0.12 6.52 0.10 6.09 0.06 6.57

TZ - 3YB 1650/30 10971 293 7.94 0.24 7.50 0.54 7.80 0.15 7.77

B 261 1100/4 12867 789 4.89 0.08 5.35 0.14 - - 5.12

B 261 1300/6 12485 218 4.79 0.07 5.15 0.12 5.38 0.08 5.11

B 261 1450/2 10587 657 4.73 0.09 5.30 0.27 - - 5.02

B 261 1550/5 10080 435 5.98 0.45 5.79 0.21 5.99 0.40 5.92

Figure 7. The dependence of the hardness of TZ-3YB and

B261 ceramics on the inverse square root of grain size.

d-1/2 (µm-1/2)

Hardness (MPa)

11 000

10 000

0.4

12 000

0.8 2.0 2.4

11 500

10 500

12 500

1.6 1.2

13 000

2.8 3.2 3.6

TZ-3YB

B261

Figure 8. Fracture toughness of TZ-3YB ceramics as a function

of grain size determined at different indentation loads.

Grain size (µm)

Fracture toughness (MPa m0.5)

6

4

0.0

8

0.4 1.6 2.0

7

5

9

1.2 0.8

10 kg load

20 kg load

30 kg load

Recently Vickers indentation fracture toughness

tests (VIF) were reviewed in detail [22]. It was concluded

that VIF techniques are not suitable for reliable

measurement of fracture toughness, KIc, because the

crack arrest process occurs in a multiple-crack environment

and in highly complex residual stress conditions.

To verify our fracture toughness results determined by

the indentation method, two standardized methods were

applied. Unfortunately, the results obtained by

"Chevron V Notch" method (CVN) and "Single Edged

V Notch Beam" method (SEVNB) showed extremely

high scatter (5-12 MPam0.5), thus it was not possible to

find any dependence on grain size. The reason for such

high variance is not clear and may be connected with

the toughening effect in TZP ceramics. From this point

of view the indentation method utilized in the present

investigation provided more consistent results compared

with the CVN and SEVNB methods.

The four-point bending strength of TZ-3YB bars

with a grain size of 0.30 µm (sintered at 1500°C/2 h)

and 0.78 µm (sintered at 1600°C/10 h) was determined

and compared. Figure 10 shows the Weibull plot of

both materials. Although the average strength of samples

varying in grain size was similar (1020 MPa vs.

1011 MPa), it can be seen in the graph that the scatter of

strength values was higher for TZ-3YB ceramics with

larger grains. This observation was confirmed by calculation

of Weibull moduli. The Weibull modulus was

m = 13.0 for ceramics with the grain size of 0.30 µm

and m = 7.54 for ceramics with the grain size of

0.78 µm. It was verified statistically that these values

are significantly different. According to the linear fracture

mechanics the body with higher fracture toughness

should possess the higher strength. In our case TZ-3YB

ceramics with a grain size of 0.78 µm had higher toughness

than ceramics with a grain size of 0.30 µm (5.88

vs. 5.17 MPam0.5). Unfortunately, the effect of higher

toughness was suppressed by an effect of bigger critical

defects due to microstructural coarsening [10]. The

competition of these two effects resulted in ceramics

with strengths apparently independent of grain size.

However, the size and distribution of defects during

coarsening cannot be efficiently controlled, which

resulted in the lower Weibull modulus for ceramics sintered

at higher temperature.

CONCLUSION

The effect of grain size on mechanical properties of

commercial submicrometre-grained 3Y-TZP ceramics

(TZ-3YB) and nanocrystalline 3Y-zirconia ceramics

(B261) was investigated. The following conclusions

could be drawn:

1.The hardness of both TZ-3YB and B261 ceramics

decreased with increasing grain size. However, the

hardness was lower in coarsened nanoceramics. This

could be attributed to different mechanisms of the

development of phase structure in nanoceramics compared

with submicrometre-grained ceramics.

2.The fracture toughness was almost constant (5.1 MPam0.5)

up to the grain size of 0.4 µm. Above this grain size,

the fracture toughness started to grow and reached the

maximum of 7.8 MPam0.5 at the grain size of 1.8 µm.

Further grain growth resulted in spontaneous transformation

from tetragonal to monoclinic phase and damage

of the samples due to cracking. Both ceramics followed

the same grain size depen-dence of fracture

toughness.

3.The four-point bending strength of TZ-3YB ceramics

with grain size of 0.30 and 0.78 µm was similar,

1020 MPa and 1011 MPa, respectively. The higher

Trunec M.

170 Ceramics − Silikáty 52 (3) 165-171 (2008)

Figure 9. Average fracture toughness of TZ-3YB and B261

ceramics as a function of grain size.

Grain size (µm)

Fracture toughness (MPa m0.5)

6

4

0.0

8

0.4 1.6 2.0

7

5

9

1.2 0.8

TZ-3YB

B261

Figure 10. Weibull plot of the bending strength data for

TZ-3YB ceramics sintered at 1500°C for 2 h and at 1600°C

for 10 h.

ln (bending strength, MPa)

ln{ln[1/(1-P)]}

-3

-5

6.6

-1

6.7 7.0 7.1

-2

-4

0

6.9 6.8

TZ-3YB - 1500°C/2 h

TZ-3YB - 1600°C/10 h 1

2

7.2

fracture toughness inherent to ceramics with larger

grain size was counterbalanced with an increase of

critical defects due to microstructural coarsening.

Moreover, the Weibull modulus declined from m = 13

at a grain size of 0.30 µm to m = 7.54 at a grain size

of 0.78 µm.

Acknowledgement

The author gratefully acknowledges the funding

provided by the Czech Ministry of Education under

grant MSM 0021630508. Dr. A. Buchal and Mrs. D.

Janova are kindly acknowledged for providing XRD

analyses and SEM images, respectively. The author

wishes to thank Mrs. Z. Skalova for her help with the

experimental work.

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Effect of grain size on mechanical properties of 3Y-TZP ceramics

Ceramics − Silikáty 52 (3) 165-171 (2008) 171

VLIV VELIKOSTI ZRN NA MECHANICKÉ

VLASTNOSTI 3Y-TZP KERAMIKY

MARTIN TRUNEC

Odbor keramiky a polymerù, Vysoké uèení technické v Brnì,

Technická 2896/2, 616 69 Brno

Mechanické vlastnosti 3Y-TZP keramiky byly zkoumány

v závislosti na velikosti zrn v rozsahu od 0,19 µm do 2,15 µm.

Vickersovy indentaèní testy byly použity pro stanovení tvrdosti

a lomové houževnatosti. Tvrdost klesala s rostoucí velikostí

zrn. Lomová houževnatost byla témìø konstantní pro keramiky

se zrny do 0,4 µm a poté rostla se zvyšující se velikosti zrn až

na 7,8 MPam0,5 u keramiky se zrny o velikosti 1,8 µm. U vìtších

zrn došlo ke spontánní transformaci tetragonální fáze na

monoklinickou. Keramické vzorky s velikostí zrn 0,30 µm a

0,78 µm mìli podobnou pevnost v ohybu, 1020 a 1011 MPa.

Mikrostrukturní zhrubnutí, které bylo nezbytné pro dosažení

vìtších zrn, vedlo k vyššímu rozptylu pevností, což se projevilo

snížením Weibullova modulu (13,0 vs. 7,54). Pro srovnání byly

také zkoumány mechanické vlastnosti nanokrystalické 3Y-ZrO2

keramiky, jejíž zrna byla zhrublá na velikost od 0,085 do

0,70 µm. Byly zjištìny rozdíly v mechanických vlastnostech

zkoumaných keramik. Možné pøíèiny tìchto rozdílù byly diskutovány.

Answer 2

Grain size has a significant influence on the mechanical properties of metals. Smaller grain sizes generally result in higher strength and hardness, as well as improved resistance to deformation and better wear characteristics. Larger grain sizes, on the other hand, tend to lead to decreased strength and ductility in metals.