WITH INCREASED LEVEL OF PROPERTIES AND PROTECTIVE LAYERS FOR NEW GENERATION

Transcription

1 DEVELOPMENT OF COMPOSITE ZIRCONIUM MATERIALS WITH INCREASED LEVEL OF PROPERTIES AND PROTECTIVE LAYERS FOR NEW GENERATION LWR ACTIVE CORE COMPONENTS S. V. Ivanova 1, E. M. Glagovsky 1, V. K. Orlov 2, I. A. Shlepov 2, K. Yu. Nikonorov 2,V.V.Rozhko 2 1 Nuclear Industrial Technology Institute of National Research Nuclear University "MEPhI 2 Joint Stock Company A.A. Bochvar High-Technology Research Institute of Inorganic Materials

2 Task New 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 structurephase or stress-strain state of zirconium items and condition of their surface.

3 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.

4 BASIC RUSSIAIN ZIRCONIUM ALLOYS The basic zirconium alloys in Russia are alloys of Zr-Nb system with 1) solid-soluble hardening : - E110 (Zr-1%Nb), - E125 (Zr-2.5%Nb), 2) solid-soluble-intermetallide hardening: alloy E635 (Zr-1%Nb ( )%Sn ( )%Fe). Mechanical properties of these alloys in recrystallized condition are given in Table 1. Table 1 Mechanical properties of zirconium alloys Alloy В Test temperature 20 С С 400 С С 0,2 В 0,2 MPa MPa % MPa MPa % E E E

5 LIQUID METAL REINFORCEMENT OF ZIRCONIUM ALLOYS Development of methods to influence characteristics of zirconium alloys due to developing their heterogeneous composite structure with dispersion principle of hardening ordered structure 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 the small amounts of super-structure (ordered) compounds thermodynamically and chemically stable in alloy preparation conditions Use of Laves phase ZrMo 2 (Т melt. =1950 С) obtaining and preserving the additional crystallization centers in the melt, Use of Laves phase ZrFe 2 (Т melt. =1675 С) releasing the strengthening component along the grain boundaries of the basic alloy. In the strongest alloy E635 the intermetallides (Zr,Nb) 3 Feand Zr(Nb,Fe) 2 are observed, and these intermetallides are formed in the alloy during processing (annealing). This work applies "direct" alloying by intermetallides and suboxides of the least strong but the most corrosion resistant alloy E110 with the aim to increase its strength properties without loss of high corrosion stability.

6 MECHANICAL PROPERTIES OF THE REINFORCED ALLOYS T, C Table 2 Comparison of mechanical properties of zirconium industrial alloys with properties of alloy E110, alloyed with intermetallides and suboxides Alloy E110 E125 E635 E110 E110+ZrFe 2 E110+Zr 2 O E110+ZrMo 2 0,2 0,2 0,2 0,2 0,2 0, Strength ( 0.2 ) of alloy E110 depending on type and quantity of alloying compounds is managed to be increased at 20 С up to 200 %; at 400 С up to 370 %, at that the alloy plasticity ( ) remains at a sufficiently high level. The obtained compositions of alloy E110 at temperatures С essentially exceed in strength the stronger alloy E125, and compositions E110+Zr 3 O and E110+ZrMo 2 even the strongest alloy E635.

7 SOLID-PHASE ALLOYING OF ZIRCONIUM ALLOYS BY FULLERENES AND CARBON NANOTUBES Carbon nanostructures, first of all, carbon nanotubes have higher capacity on hydrogen compared with physical sorption and capillary condensation. The investigations have been started on usage of nanocarbon materials to suppress hydrogen embrittlement of zirconium alloys due to ability of carbon nanotubes to hydrogen irreversible sorption. The process has been developed to modify zirconium alloys by carbon nanostructures including solid-phase alloying by fullerenes and nanotubes of matrix powders of zirconium alloys using mechanoactivation methods.

8 DEVELOPMENT OF COMPOSITE MATERIALS A promising principle to build a structural material structure with high values of: - short-term and long-term strength, - creep and fatigue resistance, - resistance to development of fatigue cracks is to make a heterogeneous structure in the material with plastic layers between strong bearing elements, i.e. a composite material development. In such composite materials (CM) the reduction of sensitivity to dynamic loads is achieved due to faster absorption of energy by CM elastic components than by plastic ones, and a decrease of sensitivity to crack formation is achieved by the intended redistribution of accumulated damages in the component which does not reduce the material bearing capacity as a whole. Composite materials were produced using a granular process. Industrial zirconium alloys E110 (system Zr Nb) and E635 (system Zr Nb Sn Fe) were used to produce composite zirconium materials.

9 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 annealing (after li att temperature t t 600 C d during i 3h hours))

10 Table 4 Annealing temperature influence on mechanical properties during stretching of composite material samples of zirconium alloys at temperature 20 С Table 3 Annealing temperature influence on mechanical properties during stretching of composite material samples of zirconium alloys at temperature 20 and 400 С Annealing temperature, = 3 h 550 С 600 С 650 С в, 0,2,, в, 0,2,, в, 0,2,, MPa MPa % MPa MPa % MPa MPa % E CM CM CM E Material Annealing temperature, = 3 h 550 С 600 С 650 С в, 02 0,2,, в, 02 0,2,, в, 02 0,2, MPa MPa % MPa MPa % MPa MPa, % E CM CM CM E aterial M

11 MECHANICAL PROPERTIES OF COMPOSITE MATERIALS The greatest gain in strength properties of CM tubes compared to E110 alloy tubes is observed in an axial direction. The increase in values В and 0,2 makes up to 25% and 40% respectively at temperature 20 С and up to 15% and 45% respectively at temperature 400 С. 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 essentially depends on CM composition and heat treatment. It can increase 3 to 45 times, at that, residual deformation is reduced 3 to 28 times.

12 CORROSION PROPERTIES OF COMPOSITE MATERIALS Fig. 3. Corrosion test results of composite materials The investigation results of CM corrosion have shown that these materials have The investigation results of CM corrosion have shown that these materials have higher corrosion resistance than alloys E110 and E635.

13 HYDROGENATION OF COMPOSITE MATERIALS Table 4 Dependence of orientation factor of hydrides on cold rolling process parameters Orientation factor of hydrides, F Cold rolling process n parameter, Q Alloy E110 tube CM tube Value of orientation factor of hydrides F n in zirconium tubes depends on cold rolling process parameter Q. According to requirements of Specifications the maximum permissible value F n in the tubes of fuel rod claddings from E110 and E635 alloys must not exceed 0.4. In CM tubes the factor F n depends much less on cold rolling process parameters that is seen in table 4.

14 SURFACE MODIFICATION OF ZIRCONIUM ITEMS Any, even insignificant, change in composition of an existing zirconium alloy with the aim to decrease its corrosion may result in decrease of other important operation properties (creep resistance and radiation growth, fatigue strength, etc.). Condition change (modification) of zirconium items surface will not result in change of item basic operation properties as modified layer thickness does not exceed several microns. However, a layer of such thickness is sufficient to increase, for example, item corrosion stability. We used 2 methods: 1) Modification of surface of zirconium items; 2) Application of certain composition coatings.

15 SURFACE MODIFICATION OF ZIRCONIUM ITEMS BY DYNAMIC IMPACT OF MICROBODIES As an alternative to applied finishing operations of mechanical and chemical cleaning of zirconium item surface we used surface cleaning by dynamic impact of microbodies applying magnetic 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 iron shot (SIS), - a powder which composition included Fe, Nb and C.

16 Investigation of corrosion stability of zirconium items with modified surface m 2 ght gain,mg/dm Wei Grinding Etching MAM by SSS MAM by SIS MAM by powder FeNbC Fig. 4. Corrosion test results of alloy E110 fuel rod cladding samples with different processing of a surface in water at temperature e 350ºC and pressure 16.5 MPa Time, days Magnetic abrasive machining results in decrease of zirconium item corrosion. The greatest positive influence on zirconium item corrosion stability is caused by MAM by split steel shot and by powder FeNbC, times reducing the corrosion compared to grinding and etching.

17 COATINGS Application of certain composition coatings on zirconium item surface can increase item corrosion resistance and decrease quantity of hydrogen absorbed by the items during operation. We have investigated vacuum ion-plasma coatings of several compositions on base of Cr and Ti applied by two methods: - electroarc sputtering; - magnetron sputtering.

18 Investigation of corrosion stability of zirconium items with protective coatings, mg/dm 2 Weight gain Initial Cr (magnetron sputtering) Cr (electroarc sputtering) CrAl CrAl-Al Ti Ti with ion mixing Fig. 4. Corrosion test results of alloy E110 fuel rod cladding samples with different coatings in water at temperature t 350ºC and pressure 16.5 MPa The investigation results have shown that Cr coatings have high corrosion resistance. Ti coatings also increase corrosion resistance of zirconium i items, but not so significantly Time, h

19 CONCLUSION Methods have been investigated to increase properties of zirconium items by modifying their structure-phase state and surface condition. The investigation results have shown the possibility to improve operation properties of the items made of existing industrial zirconium alloys and to prolong their operation duration. Depending on features of operation conditions of zirconium components and a set of operation properties necessary for their reliable operation we may use either one of the methods suggested here, for example, modification of zirconium alloy structure-phase state, or a combination of several methods of modification: structure-phase state of zirconium alloy from which the item is made and its surface. The developed modification methods can be used to increase operation properties of zirconium components of new generation LWR active cores.