Laszlo J. Kecskes 2011 TMS Annual Meeting and Conference February 27-March 4, 2011 22 Hot Explosive Consolidated Nanostructured Ta-Al Composites A. Peikrishvili,

Laszlo J. Kecskes2011 TMS Annual Meeting and ConferenceFebruary 27-March 4, 2011

22

Hot Explosive Consolidated Nanostructured Ta-Al Composites

A. Peikrishvili, L. Kecskes, E. Chagelishvili, M. Tsiklauri and B. Godibadze

2012 EPNM’12 Symposium0May 2-5, 2012, Strasbourg, France


Fabrication of Hot Explosive Consolidated Nanostructured Ta-Al Composites

ation and Properties of Hot Explosive Consolidated Ni-Al Composites

A.B. Peikrishvili, E. Sh. Chagelishvili, M.V. Tsiklauri, B. A. Godibadze and Tsulukidze Institute of Mining and Technology

Georgian Academy of Sciences

L. J. KecskesWeapons and Materials Research Directorate

US Army Research Laboratory

at

2012 EPMN’12 SymposiumMay 2-5, 2012, Strasbourg, France


Outline

• Purpose

• Technique

• Precursors

• Results• Summary of Previous Work• Current Work

• Prognosis


Background

Ta-Al precursors form a reactive system and, as a result, it is possible to conduct SHS processes.

Variants of alternative methods such as Hot ExplosiveCompaction (HEC) in combination with SHS reactions are being tried

Advantages are: short processing times, high pressures, and high temperatures

Non-toxic intermetallic replacements for various applications


Tantalum AluminidesBackground

Four intermetallicsTa2Al Tm= 2,100C;

TaAl Tm= 1,770C;

TaAl2 Tm= 1,594C;

TaAl3 Tm= 1,551C;

Tantalum Aluminides represent a ‘model’ material for the Army and Nuclear Reactors.

Equilibrium Phase Relations


Hot Explosive CompactionThe Technique

Step 1:sample were consolidated at room temperatures to

increase their predensity and to activate consolidating particles surfaces.

Step 2:Preliminary predensified billets were reloaded second

time at 950C with intensity of compression under 10GPa.

Advantages/Disadvantages:requires less energy and time than conventional

processing; but scaling is an issue


Scale-UpMotivation

The blends of coarse Al and nanoscale Ta with dimension 60-80nm were used inSubsequent experiments provided obtaining billets with dimensions 10mm × 50mm.

Ta-10Al wt.%;Al size = 10-15 µm

Ta- 50Al wt.%;Al size = 10-15 µm


1

2

3

6

4

54

7

Experimental set up for scaled-up dimensioned billets

Compaction FixtureScale Up

Furnace

Explosive Charge

Momentum Trap

SpecimenDetonator

Explosive

Momentum Trap


Compaction FixtureScale Up


Pre- and Consolidated Billets

Sample GeometryExternal Appearance


Ta-Al HEC BilletsCross Sections

• Ta75.88 Nb24.12

• Ta83.44 Nb16.56


Mechanical and Electrical Properties of HEC Ta–Al Composites

c.

. In Figure there is presented the results of measurement of mechanical properties (elasticity Young modulus – E, relaxation Q-1 (Q is the quality factor of vibrating sample) for HEC Ta-Al composites. It is seen the considerable changes in their mechanical and electrical properties depending on compositions. In particular, the larger relaxation maximum for Ta 50 % - Al 50 % composition could be apparently related with relaxation on grain boundaries. In this case the peak height depends on the area of grains which is maximal when the volume ratios of both phases are equal. Besides it, the formation new aluminade phases could contribute this effect what should be tested by additional X-ray measurements which are under way


Mechanical and Electrical Properties of HEC Ta–Al Composites

Correspondingly, this effect in mechanical properties is accompanied by a considerable increase in resistivity and resistivity temperature factor for Ta 50 % - Al 50 % composition..


Ta-10%Al HEC BilletsStructure – Billet#1

Billet #1; 90/10; 950C Billet #1; 90/10; 950C

Blend Blend


Ta-50%Al HEC BilletsStructure – Billet#2

Billet #2; 50/50; 950C Billet #2; 50/50; 950C

Blend Blend


Ta-Al HEC BilletsPhase Chemistry Precursors

Al precursor


Ta-Al HEC BilletsPhase Chemistry – Precursors

Ta precursor


Ta-Al HEC BilletsPhase Chemistry - Products

Billet #2; 50/50; 950CBillet #1; 90/10; 950C


Billets #1&2; 90/10 & 50/50; 9500C

Ta-Al HEC BilletsX-ray diffraction picture


Previous results connected with HEC Ni-Al and Ti-Al composites, the current application of HEC to Ta-Al composites seems to be promising. It was shown in our previous work that application of high temperatures and HEC of composites of Ni(Ti)-Al could not fully result in intermetallic compounds. HEC of Ni-Al composites at 1000C in spite of having good density and correct geometry provided only, resulted only partially of intermetallic compounds of Ni-Al composites.

Analyzing the situation of the formation of intermetallics it was concluded that the reason is low intensity of compression due to low pre-density of the HEC precursors.

In contrast to Ni(Ti)-Al composites, the use of Ta-Al precursors seems to be more promising, from the standpoint of features of explosive consolidation processes and formation of intermetallic compounds. This is the high density of Ta powder (16.4 g/cm3) and the high reactivity of Ta-Al system. Application of HEC technology may be solved previously fixed problems, based on developed of high intensity of compression (loading) and high consolidation needed for initiation of SHS processes during heating.

Ta-Al HEC BilletsDiscussion


Results of the X-ray investigation show that in contrast to pure Ta & Al diffraction of the precursors, the Ta-Al HEC samples have different phase content. It is difficult to recognize and identify the pure Ta and Al phases.

The appearance of new lines of Ta-10%Al & Ta-50%Al composites indicates that there were chemical reactions and intermetallic compounds formed.

Unfortunately, because of pure database for X-ray analyses and short period before EPNM’11 symposium, correct identification of the as-formed intermetallics in the Ta-Al system was not yet possible.

Ta-Al HEC BilletsDiscussion


Billet 1 Ta-10%Al T=950C 100g load

Hardness 126.64 (70.9-286.7)

Billet 2 Ta-50%Al T=900C 50g load

Hardness 261.5 (31.9-306.9)

Ta-Al HEC BilletsHardness Measurements


Interim Summary

In whole taking into account the obtained results undoubtedly may be underline of advantages of application Ta based precursors in explosive consolidation technology due to their high density, high elasticity and high reactivity. The all mentioned characteristics provides development of high intensity of dynamic compression, essentially to increase the plastic flow of consolidated grain surfaces and easier formation of rigid common boundaries between the separate grains and syntheses of new intermetalic compounds.

The results presented in current report may be considered as a preliminary results prepared personally for EPNM’11 symposium showing some advantages of application Ta-Al precursors in contrast to another reactive systems such as Ni-Al and Ti-Al. The preliminary investigation shows that application of nanoscale Ta-Al precursors in HEC technology allows to fabricate high dense billets without cracks and formed intermetallic compounds when in case of coarse Ni(Ti)-Al precursors it was impossible.


Future Work

Improve particle size matching and achieve full consolidation

Increase Al content of Ta(Al)

Modify relative ratio of precursors and intermetallics in scaled up products

Documents

Laszlo J. Kecskes 2011 TMS Annual Meeting and Conference February 27-March 4, 2011 22 Hot Explosive Consolidated Nanostructured Ta-Al Composites A. Peikrishvili,