DEVELOPMENT OF COMPOSITE ZIRCONIUM MATERIALSDEVELOPMENT OF COMPOSITE ZIRCONIUM MATERIALS WITH INCREASED LEVEL OF PROPERTIES AND PROTECTIVE LAYERS FOR NEW GENERATION

LWR ACTIVE CORE COMPONENTSLWR ACTIVE CORE COMPONENTS S. V. Ivanova1, E. M. Glagovsky1, V. K. Orlov2, I. A. Shlepov2,

K. Yu. Nikonorov2, V. V. Rozhko2K. Yu. Nikonorov , V. V. Rozhko

1 Nuclear Industrial Technology Institute of National Research Nuclear University "MEPhI”y

2 Joint Stock Company “A.A. Bochvar High-Technology Research Institute of Inorganic Materials”

TaskNew generation LWR more rigid operation conditions zirconium alloys with increased

level of properties

It was analyzed traditional methods used to change properties of metals and alloys:1) selection of alloying elements and their quantity;2) choice of annealing and tempering optimum modes;3) use of thermo-mechanical treatment different methods.

Aim:To develop methods to increase operation properties of existing industrial zirconium

alloys (without changing alloy composition) and items made thereof.

This task can be solved: by changing the zirconium alloy composition – developing new zirconium alloys or

modifying existing ones; without changing the existing zirconium alloy composition, but by modifying only structure-

phase or stress-strain state of zirconium items and condition of their surface.

MODIFICATION OF ZIRCONIUM ALLOYS

Methods that we used for modification of zirconium alloys :

liquid metal reinforcement by ordered structures, solid phase alloying by fullerenes and carbon nanotubes; granular metallurgy.

BASIC RUSSIAIN ZIRCONIUM ALLOYS

The basic zirconium alloys in Russia are alloys of Zr-Nb system with1) solid-soluble hardening :

- E110 (Zr-1%Nb),- E125 (Zr-2 5%Nb)- E125 (Zr-2.5%Nb),

2) solid-soluble-intermetallide hardening: alloy E635 (Zr-1%Nb (1.1-1.4)%Sn–(0.3-0.5)%Fe).Mechanical properties of these alloys in recrystallized condition are given in Table 1.

T bl 1Table 1Mechanical properties of zirconium alloys

Test temperature20С 400СAlloy 20 С 400 С

ВMPa

0,2MPa

%

ВMPa

0,2MPa

%

E100 350 200 30 180 90 38E125 450 280 28 270 180 22E125 450 280 28 270 180 22E635 590 500 16 288 253 18

LIQUID METAL REINFORCEMENT OF ZIRCONIUM ALLOYSDevelopment of methods to influence characteristics of zirconium alloys due to developingDevelopment of methods to influence characteristics of zirconium alloys due to developingtheir heterogeneous composite structure with dispersion principle of hardening orderedstructure compounds are used as a hardening phase

using a casting process due to liquid metal reinforcement

an alloy transfer in some localized volumes into an ordered state by introducing in a melt thesmall amounts of super-structure (ordered) compounds thermodynamically and chemicallystable in alloy preparation conditions

Use of Laves phase ZrMo (Т =1950 °С) obtaining and preserving the additionalUse of Laves phase ZrMo2 (Тmelt.=1950 С) obtaining and preserving the additionalcrystallization centers in the melt,Use of Laves phase ZrFe2 (Тmelt.=1675 °С) releasing the strengthening component alongthe grain boundaries of the basic alloy.

I th t t ll E635 th i t t llid (Z Nb) F d Z (Nb F ) b d dIn the strongest alloy E635 the intermetallides (Zr,Nb)3Fe and Zr(Nb,Fe)2 are observed, andthese intermetallides are formed in the alloy during processing (annealing).

This work applies "direct" alloying by intermetallides and suboxides of the least strong but themost corrosion resistant alloy E110 with the aim to increase its strength properties withoutl f hi h i t bilitloss of high corrosion stability.

MECHANICAL PROPERTIES OF THE REINFORCED ALLOYS

Table 2Comparison of mechanical properties of zirconium industrial alloys with properties

of alloy E110, alloyed with intermetallides and suboxides

Alloy

T,°C

E110 E125 E635

E110 E110+ZrFe2 E110+Zr2O E110+ZrMo2

0,2 0,2 0,2 0,2 0,2 0,2 20 200 30 376 20 580 22 606 23 280 28 500 16400 90 38 210 24 333 24 420 18 180 22 253 18400 90 38 210 24 333 24 420 18 180 22 253 18

Strength (0.2) of alloy E110 depending on type and quantity of alloying compounds ismanaged to be increased at 20С up to 200 %; at 400С – up to 370 %, at that the alloyplasticity () remains at a sufficiently high level.

The obtained compositions of alloy E110 at temperatures 20-400С essentially exceed instrength the stronger alloy E125, and compositions E110+Zr3O and E110+ZrMo2 even thestrongest alloy E635.

SOLID PHASE ALLOYING OF ZIRCONIUM ALLOYSSOLID-PHASE ALLOYING OF ZIRCONIUM ALLOYS BY FULLERENES AND CARBON NANOTUBES

Carbon nanostructures, first of all, carbon nanotubes have higher capacity on hydrogencompared with physical sorption and capillary condensation.

The investigations have been started on usage of nanocarbon materials to suppresshydrogen embrittlement of zirconium alloys due to ability of carbon nanotubes to hydrogenirreversible sorption.

The process has been developed to modify zirconium alloys by carbon nanostructuresincluding solid phase alloying by fullerenes and nanotubes of matrix powders of zirconiumincluding solid-phase alloying by fullerenes and nanotubes of matrix powders of zirconiumalloys using mechanoactivation methods.

DEVELOPMENT OF COMPOSITE MATERIALSDEVELOPMENT OF COMPOSITE MATERIALS

A promising principle to build a structural material structure with high values of:- short-term and long-term strength,

d f ti i t- creep and fatigue resistance,- resistance to development of fatigue cracksis to make a heterogeneous structure in the material with plastic layers between strongbearing elements, i.e. a composite material development.

In such composite materials (CM) the reduction of sensitivity to dynamic loads is achieveddue to faster absorption of energy by CM elastic components than by plastic ones, and adecrease of sensitivity to crack formation is achieved by the intended redistribution ofaccumulated damages in the component which does not reduce the material bearingcapacity as a whole.p y

Composite materials were produced using a granular process.

Industrial zirconium alloys E110 (system Zr–Nb) and E635 (system Zr–Nb–Sn–Fe) wereused to produce composite zirconium materials.

Fig. 1 Microstructure of a composite material with composition CM 2 (after annealing at temperature 600 C during 3 hours)

Fig. 1 Microstructure of a composite material with composition CM 2 (after annealing at temperature 600 C during 3 hours)

STRUCTURE OF COMPOSITE MATERIALS

Fig. 1. Microstructure of a composite material with composition CM 2 (after annealing at temperature 600 C during 3 hours)

Fig. 2. Microstructure of a composite material with composition CM 3 ( ft li t t t 600 C d i 3 h )(after annealing at temperature 600 C during 3 hours)

Table 4 Annealing temperature influence on mechanical properties during stretching of composite material samples of zirconium alloys at temperature 20С

Table 4 Annealing temperature influence on mechanical properties during stretching of composite material samples of zirconium alloys at temperature 20С

Table 4 Annealing temperature influence on mechanical properties during stretching of composite material samples of zirconium alloys at temperature 20С

Table 4 Annealing temperature influence on mechanical properties during stretching of composite material samples of zirconium alloys at temperature 20С

Table 4 Annealing temperature influence on mechanical properties during stretching of composite material samples of zirconium alloys at temperature 20С

Annealing temperature = 3 h

Table 3Annealing temperature influence on mechanical properties during stretching of composite

material samples of zirconium alloys at temperature 20 and 400С

Mat

eria

l Annealing temperature, = 3 h550С 600С 650С

в, MPa

0,2, MPa

, %

в, MPa

0,2, MPa

,%

в, MPa

0,2, MPa

, %

E110 412 417 319 324 45 47 393 407 299 306 43 46 382 401 279 289 41 45E110 412-417 319-324 45-47 393-407 299-306 43-46 382-401 279-289 41-45CM 1 614-624 493-521 24-27 493-512 391-414 34-35 456-484 353-381 30-38CM 2 595-624 484-512 23-27 495-521 395-423 33-34 475-485 368-381 31-36CM 3 688-698 521-558 20-23 559-586 432-451 25-32 521-539 418-428 25-33E635 474 504 381 390 37 39 479 489 365 390 35 38 463 468 339 355 34 38E635 474-504 381-390 37-39 479-489 365-390 35-38 463-468 339-355 34-38

ater

ial Annealing temperature, = 3 h

550С 600С 650Св, 0 2, , в, 0 2, , в, 0 2, %M

в,MPa

0,2, MPa

, %

в, MPa

0,2, MPa

, %

в, MPa

0,2, MPa , %

E110 181-191 112-117 49-52 181-196 107-118 51-53 180-191 103-113 40-44CM 1 363-372 321-345 23-28 218-223 149-159 48-51 205-218 135-150 32-37CM 2 358 372 331 345 22 26 232 242 167 201 40 44 213 223 144 172 32 35CM 2 358-372 331-345 22-26 232-242 167-201 40-44 213-223 144-172 32-35CM 3 360-396 350-372 21-22 260-288 195-219 39-43 232-256 167-190 28-33E635 268-272 180-190 40-43 257-273 180-185 42-43 241-247 157-161 33-38

MECHANICAL PROPERTIES OF COMPOSITE MATERIALS

The greatest gain in strength properties of CM tubes compared to E110 alloy tubes isobserved in an axial direction. The increase in values В and 0,2 makes up to 25% and 40%В 0,2respectively at temperature 20С and up to 15% and 45% respectively at temperature 400С.At that, maximal drop in plasticity does not exceed 5%.

CREEP RESISTANCE OF COMPOSITE MATERIALS

In axial direction the creep resistance of CM tubes compared to E110 alloy tubes essentiallydepends on CM composition and heat treatment. It can increase 3 to 45 times, at that,p p , ,residual deformation is reduced 3 to 28 times.

CORROSION PROPERTIES OF COMPOSITE MATERIALS

Fig. 3. Corrosion test results of composite materials

The investigation results of CM corrosion have shown that these materials haveThe investigation results of CM corrosion have shown that these materials have higher corrosion resistance than alloys E110 and E635.

HYDROGENATION OF COMPOSITE MATERIALS

Table 4

Cold rolling process parameter, Q

Orientation factor of hydrides, Fn

Alloy E110 tube CM tube

Table 4Dependence of orientation factor of hydrides on cold rolling process parameters

p , Alloy E110 tube CM tube0.54 0.6 0.10.75 0.5 0.10.87 0.4 0.11.6 0.4 0.12.8 0.4 0.13.8 0.2-0.3 0.1

Value of orientation factor of hydrides Fn in zirconium tubes depends on cold rolling processparameter Q.According to requirements of Specifications the maximum permissible value Fn in the tubes offuel rod claddings from E110 and E635 alloys must not exceed 0.4. In CM tubes the factor Fng y ndepends much less on cold rolling process parameters that is seen in table 4.

SURFACE MODIFICATION OF ZIRCONIUM ITEMSSURFACE MODIFICATION OF ZIRCONIUM ITEMS

Any, even insignificant, change in composition of an existing zirconium alloy withthe aim to decrease its corrosion may result in decrease of other importantthe aim to decrease its corrosion may result in decrease of other importantoperation properties (creep resistance and radiation growth, fatigue strength, etc.).

Condition change (modification) of zirconium items surface will not result in changeof item basic operation properties as modified layer thickness does not exceedseveral microns. However, a layer of such thickness is sufficient to increase, forexample, item corrosion stability.

We used 2 methods:1) Modification of surface of zirconium items;2) Application of certain composition coatings.

SURFACE MODIFICATION OF ZIRCONIUM ITEMS BY DYNAMIC IMPACT OF MICROBODIESBY DYNAMIC IMPACT OF MICROBODIES

As an alternative to applied finishing operations of mechanical and chemical cleaning ofzirconium item surface we used surface cleaning by dynamic impact of microbodies applyingzirconium item surface we used surface cleaning by dynamic impact of microbodies applyingmagnetic abrasive machining (MAM).

This method of processing can act a double part:1) remove manufacture products from the surface of zirconium items;)2) modify and microalloy the surface.

Microbodies of three compositions were used for magnetic abrasive machining:split steel shot (SSS)- split steel shot (SSS),

- split iron shot (SIS),- a powder which composition included Fe, Nb and C.

Investigation of corrosion stability of zirconium items with modified surface

25

20

25

m2

Grinding

Etching

Fig. 4. Corrosion test results of alloy E110

fuel rod cladding l ith

10

15

ght g

ain,

mg/

dm

Etching

MAM by SSS

MAM by SIS

MAM b d

samples with different processing of a surface in water

at temperature

5

Wei MAM by powder

FeNbC

a e pe a u e350ºC and pressure

16.5 MPa

00 5 10 15 20 25 30 35

Time, days

Magnetic abrasive machining results in decrease of zirconium item corrosion. The greatest positive influence on zirconium item corrosion stability is caused by MAMgreatest positive influence on zirconium item corrosion stability is caused by MAM by split steel shot and by powder FeNbC, 1.5-2.0 times reducing the corrosion compared to grinding and etching.

COATINGSCOATINGS

Application of certain composition coatings on zirconium item surface canincrease item corrosion resistance and decrease quantity of hydrogen absorbedincrease item corrosion resistance and decrease quantity of hydrogen absorbedby the items during operation.

We have investigated vacuum ion-plasma coatings of several compositionson base of Cr and Ti applied by two methods:- electroarc sputtering;- magnetron sputtering.

Investigation of corrosion stability of zirconium items with protective coatings

Fig. 4. Corrosion test results of alloy E110 fuel rod cladding

samples with different coatingsi t t t t 350ºC

21

24

27

in water at temperature 350ºC and pressure 16.5 MPa

15

18

Initial

Cr (magnetron sputtering)

Cr (electroarc sputtering), mg/

dm2

The investigation results have shown that Cr coatings have high corrosion resistance. Ti coatings also increase corrosion

i t f i i it b t t6

9

12Cr (electroarc sputtering)

CrAl

CrAl-Al

Ti

Ti with ion mixing

Wei

ght g

ain

resistance of zirconium items, but not so significantly.

-3

0

3

0 50 100 150 200 250

3Time, h

CONCLUSION

Methods have been investigated to increase properties of zirconium itemsby modifying their structure-phase state and surface condition.The investigation results have shown the possibility to improve operationg p y p pproperties of the items made of existing industrial zirconium alloys and toprolong their operation duration. Depending on features of operationconditions of zirconium components and a set of operation propertiesnecessary for their reliable operation we may use either one of thenecessary for their reliable operation we may use either one of themethods suggested here, for example, modification of zirconium alloystructure-phase state, or a combination of several methods of modification:structure-phase state of zirconium alloy from which the item is made andp yits surface.The developed modification methods can be used to increase operationproperties of zirconium components of new generation LWR active cores.