Hot Explosive Consolidated Nanostructured Ta-Al Composites 22 Hot Explosive Consolidated Nanostructured Ta-Al Composites A. Peikrishvili, L. Kecskes, E. Chagelishvili, M. Tsiklauri and B. Godibadze 2012 EPNM’12 Symposium0 May 2-5, 2012, Strasbourg, France

ation and Properties of Hot Explosive Consolidated Ni-Al Composites 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. Kecskes Weapons and Materials Research Directorate US Army Research Laboratory at 2012 EPMN’12 Symposium May 2-5, 2012, Strasbourg, France 2

Outline Purpose Technique Precursors Results Summary of Previous Work Current Work Prognosis 2

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 Explosive Compaction (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 Aluminides Background Tantalum Aluminides represent a ‘model’ material for the Army and Nuclear Reactors. Equilibrium Phase Relations Four intermetallics Ta2Al Tm= 2,100C; TaAl Tm= 1,770C; TaAl2 Tm= 1,594C; TaAl3 Tm= 1,551C;

Hot Explosive Compaction The 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-Up Motivation The blends of coarse Al and nanoscale Ta with dimension 60-80nm were used in Subsequent experiments provided obtaining billets with dimensions 10mm × 50mm. Ta-10Al wt.%; Al size = 10-15 µm Ta- 50Al wt.%; Al size = 10-15 µm

Compaction Fixture Scale Up Experimental set up for scaled-up dimensioned billets Detonator Specimen 1 2 3 6 4 5 7 Furnace Explosive Explosive Charge Momentum Trap Momentum Trap

Compaction Fixture Scale Up

Pre- and Consolidated Billets Sample Geometry External Appearance Pre- and Consolidated Billets

Ta-Al HEC Billets Cross Sections Ta75.88 Nb24.12 Ta83.44 Nb16.56

Mechanical and Electrical Properties of HEC Ta–Al Composites . 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 Billets Blend Blend Structure – Billet#1 Billet #1; 90/10; 950C Billet #1; 90/10; 950C Blend Blend

Ta-50%Al HEC Billets Blend Blend Structure – Billet#2 Billet #2; 50/50; 950C Billet #2; 50/50; 950C Blend Blend

Phase Chemistry Precursors Ta-Al HEC Billets Phase Chemistry Precursors Al precursor

Phase Chemistry – Precursors Ta-Al HEC Billets Phase Chemistry – Precursors Ta precursor

Phase Chemistry - Products Ta-Al HEC Billets Phase Chemistry - Products Billet #2; 50/50; 950C Billet #1; 90/10; 950C

X-ray diffraction picture Ta-Al HEC Billets X-ray diffraction picture Billets #1&2; 90/10 & 50/50; 9500C

Ta-Al HEC Billets Discussion 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 Billets Discussion 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.

Hardness Measurements Ta-Al HEC Billets Hardness Measurements 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 261.5 (31.9-306.9)

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