Shock Consolidation of Powders – Theory and Experiment

A recently proposed model of shock consolidation of powders quantitatively predicts regimes of input energy and shock duration required to produce well-bonded compacts. A growing data base from shock experiments in which the shock wave and powder parameters of importance are controlled allows evaluation of the model. Rapidly solidified crystalline AISI 9310, and microcrystalline Markomet 3.11, as well as amorphous Markomet 1064 and crystalline Mo powders, have been consolidated by shocks up to 2 μsec duration. The formation of amorphous layers on Marko 3.11 particle surfaces indicates that surface melting and rapid solidification occurred. Decreasing amounts of amorphous structure are retained in Marko 3.11 and 1064 powder compacts with increasing shock energies. Significant improvement in Mo particle bonding is achieved by reducing surface oxides prior to shock consolidation

The Effect of Shock Duration on the Dynamic Consolidation of Powders

A recently advanced model for the shock consolidation of powders predicts, for a powder of given distension, the regimes of shock pressure and shock duration expected to yield fully densified compacts of near optimum strength. The model is evaluated in terms of UTS measurements in compacts of rapidly solidified powders of AISI 9310 alloy, shocked to initial shock pressures between 3.6 and 17.9 GPa and to shock durations between 0.23 and 2.1 μs. We find that in powders of distention 1.7, shock durations > 1 μs are required at 10 GPa to properly solidify the melt

A theory for the shock-wave consolidation of powders

A model for the shock consolidation of powders is developed which predicts, for a given powder density, the regimes of shock pressure P and shock duration t_d expected to yield fully densified compacts of near optimum strength. Most of the densification work is assumed deposited near particle boundaries, leading to partial melting. The model gives an upper bound to the amount of melt. The condition that the melt between particles must exceed a critical thickness and must solidify within the duration of the shocked state leads to necessary conditions for P and t_d.These requirements are presented in “maps of shock consolidation,” using normalized parameters. The model predicts that for a shock energy (normalized to that required to heat iron to the melting point) of 0.7, a minimum shock duration of 2μs is required to consolidate 60μm diameter iron-based powder

Shock consolidation of a rapidly solidified steel powder

Rapidly solidified AISI 9310 steel powders were consolidated by shock waves produced from the impact of high velocity flyers. Dependence of the microhardness and the ultimate tensile strength of the compacts on the initial shock pressure (from 3.6 to 17.9 GPa) and the maximum shock pressure (from 6 to 37 GPa) was measured for an initial powder density 0.6 of the bulk density and a shock duration of 2–3 s. Photomicrographs and SEM fractographs were used to study the interparticle bonding in the compacts. Results show that for initial shock pressures below 4 GPa, the compacts have negligible strength. However, above this threshold the strength of the compact rises rapidly until a maximum value of 1.3 ± 0.1 GPa is reached for an initial shock pressure of 12.4 GPa. The strength then remains constant before decreasing at the highest initial shock pressure. In marked contrast, with increasing shock pressure, the diamond pyramid hardness increases very gradually from a value of about 340 for the powder to about 500 at the highest shock pressure. The maximum strength obtained correlates reasonably well with the strength-expected from microhardness measurements

Shock Compaction of Molybdenum Powder

Incident shocks varying from 9 to 12 GPa and 2 µs duration, impinging on porous pure Mo (100 µm) powder of distension 1.4, are found to produce compacts of at least 99.4% of crystal density. Although recovered samples are consolidated and exhibit diamond pyramid hardness of ~330 to 400, the particles do not appear to be well bonded. Among several possible models for producing a melt layer on particles vie propose a dynamic frictional model. The shock pressures required to produce a ~1 µm film of molten material as a result of dynamic friction varies from 11 to 108 GPa for grain sizes of 100 to 10 µm

Influence of Ovarian Side and Initiation Time of First Aspiration with Relation of Transvaginal Follicular Aspiration in HF x Sahiwal Cows

This study was carried out to observe the influence of ovarian side and initiation time of first aspiration during OPU programme in HF X Sahiwal cows. Eight cows were randomly divided in to two groups (A and B) each consisting of 4 donors. Follicular aspiration was initiated on day 4 (first follicular wave) and day 13 (second follicular wave) of estrous cycle, respectively. From group-A donors, total 200 follicles were aspirated in eight sessions with a mean of 6.25 ± 2.05 per animal per session of which 52.50 (105/200) and 47.50 (95/200) per cent follicles were from left and right ovary, respectively. The mean numbers of small, medium and large follicles aspirated were 2.06 ± 0.87, 2.65 ± 0.88 and 1.53 ± 0.91 with the recovery rate of 33.0 (66/200) (3–5 mm), 42.50 (85/200) (6–9 mm) and 24.50 (49/200) (=10 mm) per cent, respectively. From group-B donors, total 179 follicles were aspirated of which 48.60 (87/179) and 51.40 (92/179) per cent follicles were from left and right ovary, respectively. The mean number of aspirated follicles per cow per session from group-B donor cows was 5.59 ± 1.03 and the mean numbers of small, medium and large follicles aspirated 1.87 ± 0.96, 2.5 ± 0.66 and 1.25 ± 0.64 with the recovery rate of 34.07 (61/179), 44.94 (80/179) and 21.22 (38/179) per cent, respectively. The number of follicles from left and right ovaries of different categories among group A and B donor cows did not differ significantly (P>0.05). This study showed that there cows no any influence of ovarian side and initiation time on follicular aspiration. [Vet. World 2010; 3(6.000): 286-288