Crystal Growth Mechanism of DD8 Nickel-based Superalloy Single Crystals

Grains that deviate from the direction of heat flow can eliminate crystal grains that are preferentially grown in the direction parallel to the heat flow. Studies have shown that the process of grain elimination in the preparation of nickel-base superalloy single crystals does not depend on the preferred growth crystal orientation parallel to the heat flow direction. It is the relative position of the crystal dendrites. This is a good explanation for the phenomenon of growth of stray crystals outside the predetermined orientation that often occurs during the preparation of high-temperature alloy single crystals. Single-crystal blades have better performance than ordinary equiaxed and unidirectionally solidified blades.坫 Gas turbines are the preferred choice for gas turbines, and the preparation of single crystal leaves often encounters the integrity of single crystals, especially heterocrystallites. 381. The theory of traditional crystal growth theory believes that 19 grain competitions in the twinning preparations1 As long as the grain is grown in a preferred manner and the body is called and heat flowed, this grain will inhibit grain growth in the other direction and eventually grow. For the best growth of crystal orientation and heat flow in the direction of the miscellaneous crystals, literature 10. From the perspective of the dimension of the different grades of crystal growth of sub-order and higher dendrite to make grain interface migration caused. Shen received the initial date of the year 1999062 Received the revised manuscript date 19990923 Author brief introduction Liu Zhiyi. Male, born in 1962. professor. The conclusion of the postdoctoral decomposing infers that if the secondary branch of the crystal grain is oriented, the result of grain growth can be independent of the direction of the secondary dendrite, the orientation of the civilian direction and the direction of heat flow, and the reason why the mixed crystal can grow up. It is explained.

We have not designed a double-grain competition test to verify the validity of the reasoning that the preferred growth product is a deviation from the direction of heat flow that eliminates the preferential growth of the preferred growth product to the direction of heat flow.

1 Experimental method for experimentation! 8 Nickel-based high-temperature gold academic composition score score. , 50, the bar stock to test the mother alloy. The bulk 008 single crystals prepared by the crystal selection method were subjected to a ray diffractometer to measure the crystal orientation, and then cut into different crystal orientations using a wire cutting method, and the size was a semi-cylindrical seed crystal with a diameter of 6.9 ml×20 mm, and The method is paired with a group for double-particle coupled competitive growth experiments. The matched seed crystal and the master alloy rod are loaded into a corundum tube with a diameter of 7 mm, heated to 1548.C on a high temperature gradient LMC vacuum directional solidification apparatus, and kept for 15 min, and oriented with G=250 Kcm=47.6,3. The solidified twin grains compete for growth and the pulling speed is controlled by a microcomputer. The cross-section and longitudinal section of the sample were cut off, and the results of grain competition and grain boundary migration were observed on a 2 to 8 light microscope, and the area fraction of the crystal grains on each section was measured with a 2 image analyzer.

2 Experimental results Metallographic observation showed that grain growth was competitive with a seed crystal of 1. Grains with preferred grain growth directions of 100 and heat flow eliminated crystal grains with a preferred growth direction deviating from the direction of heat flow by 45, 2, by 1 With the seed crystals, preferentially growing crystal grains deviated from the direction of the heat flow eliminates the grain growth of the preferred growth product toward the direction of 100 and heat flow, such as crystal orientation 100> deviated from the direction of heat flow eliminated the preferential growth crystal direction 100 and heat flow Direction-induced grain, 4 Determination of the area fraction of the cross-section, according to the 13 seed crystals, the fastest rate of grain elimination; according to the match, the speed of grain elimination between them, 5. Observation of grain boundary migration found that The grain boundary migration velocity on the cross-section is uneven across the interface, Liu Zhiyi et al., 8 Nickel-Rhenium-Growth, Growth of Alloying Single Crystals, Growth of Bulk Crystals, and Growth of Bulk Crystals Results 6 sets of twin-crystal, surface metallographic photographs. The corresponding crystal ocean migration 3 points pray and discuss 3.1 The analysis of the mechanism of heterocrystal growth can be seen from 2. The preferred growth direction of the crystal is 100% away from the heat flow and grows during growth. This is due to the traditional theory of crystal growth.

The result of 4 is that the grain of the preferred growth direction deviated from the direction of hot flooding grew up in the competitive growth. Grains with preferential growth direction and heat flow direction are eliminated, and a long seed crystal has a preferred growth direction of the seed crystal called 0 and heat flow direction. However, the relative crystal orientations of the double grains of each group are different, ie, the secondary dendrites of each group of double grains. The dimension of the secondary dendrite is relatively different, its meaning is like Tian. 7.

On the left side of 7 the crystal growth preferentially crystallizes towards the secondary branch crystal parallel to the heat flow direction. Wherein the sub-crystals are perpendicular to the two coupled crystal faces. On the other hand, the preferential crystal growth of the right crystal grain deviates from the direction of the heat flow in the direction of 45. The interface between the subdendritic crystal and the two crystallites is 45°, and the other is parallel to the crystal grain boundary. The relative position of such dendrites allows the secondary dendrites of the left grains to grow above the secondary dendrites of the right grains. Block the growth of the right crystal secondary dendrites. And the growth of secondary dendrites makes the crystallite interface to the right. As a result, the left grain grows and the right grain gradually disappears. This is the result of 2 if the result is a traditional crystal. Long theory to explain. The reason for this is that the direction of the secondary dendrite of the left crystal grain, ie, the preferential growth of the crystal growth direction toward the heat flow, produces a faster growth rate, so that other preferred growth crystal grains can be eliminated from the direction of the heat flow. This article analyzes differences.

Although it is not possible to make a judgment based on the result of the matching of the seed length of only 1 seed. However, a comprehensive explanation of the seed crystal growth of 10 can be obtained.

According to the seed crystal matching method, the relative position of the dendrite should not be 7. Zhai Zhongming, the preferred crystal of the left crystal is still flat to the direction of the tenth heat flow, but then the dendrite becomes an angle of 4 to 45 with the coupled grain boundary. While the eutectic growth crystals of the edge crystals are still deviated from the direction of the heat flow in the subdendritic crystals, the secondary dendrite crystals on the twin interface side become perpendicular to the grain boundaries. This relative positional relationship allows the right dendrites to have a chance to insert between the secondary branches of the left crystal and then grow two secondary products. The growth direction of the secondary dendrite is parallel and perpendicular to the secondary branch. The crystals are all perpendicular to the secondary dendrites. In this way, their growth can just occupy the space above the secondary dendrites of the left crystal, hindering the growth of the secondary dendrites from the left crystal sub-crystal, and shifting the crystal interface to the left crystal grains. As a result, the right crystal grain grows and the left crystal grain is gradually eliminated.

And sub-dendrites still maintain 71 orientation, edge grained. The secondary dendrites and secondary branches become the orientation of the right grain in 7;1. This dendritic phase pays ancient times so that the secondary dendrites of the side grains can lean against the secondary branch of the left product, and the parallel branches of the grain boundaries are parallelized by the left branch. Above the secondary dendrite, its growth is blocked, so that the left grain migration at the grain interface 4 is completed, and finally the right grain grows. The left grain is gradually eliminated, such as Wai 4.

Therefore, from the above analysis, it can be seen that the key factor in grain competition growth is not whether the preferred growth crystal to the secondary branch product is parallel to the heat flow direction, but whether the relative position support of the crystal dendrite can suppress the opposite crystal grain times. The length of dendrites. This is also the root cause of the fact that some of the actual dust produced in nickel-base superalloy single-products may grow in the way that the preferred growth crystals deviate from the direction of heat flow to survive and grow.

3.2 The test result of the relationship between the interfacial area fraction and the pull distance in the interfacial migration interface shows that the 1;1 collocation method has the slowest migration speed. The speed of the interface migration generated by the seed crystals is between them.

The analysis in Section 3.1 of the team can tell that in the competitive grain growth of two grains under a seed crystal matching method, the secondary dendrite directly suppresses each other. The dendrites of the dendrite, and the secondary dendrites parallel to the lower heat flow direction produced a faster collocation, although the secondary dendrite was also directly suppressed by the secondary dendrites, resulting in a lower seed crystal matching pattern than 13 The rate of elimination was low at the interface, and the rate of migration at the interface was 4; however, the timing of the dendrite growth at the 3 seed crystals was later than that of the secondary dendrites, and it took longer time than the secondary dendrites. This naturally affects the speed at which winning wafers are eliminated. Together with its superior crystal sub-branched dendrite, it deviates from the heat flow direction by 45 degrees. Reduced the grain synthesis effect to show the lowest interface migration rate.

The microscopic process from the interface can also be seen. In the cross-section of the 13 seed crystals with which the grain competition grows, the velocity at the interface is not different from the growth of the secondary dendrite spacing. This results in dendrite misalignment in some places on the grain interface. The products are on top of each other. In places where they are misaligned, the interface is rapidly advancing, and where mutual payment is made, interface migration is hindered. Therefore, the migration of 6,1 interface is not observed.

In the longitudinal section where the crystal grain competition is based on rudder crystals, the migration of grain boundaries is also non-linear, and it will be repeated in some places, but the general trend of interface advancement will not change. 6 The reason for this phenomenon is that the secondary dendrites are roughly angularly equidistant from the cross-section, which makes it possible for the dendrites of the superior crystal grains that grow at the denuded crystal grains at the original grain interface to be eliminated. The hindrance of the crystallite-level dendrite, when the crystal dendrite is eliminated occupies a favorable position, the grain interface migration will occur repeatedly. However, the repetition is limited because the superior crystal grain dendrite grown in the dendrite where the dendrite crystals are misaligned will rapidly grow laterally and grow into the secondary dendrite crystals that branch in the secondary dendrite.

Even at the original breakthrough, the hole code of the dendritic crystals at the lower level was found. Because of the different crystal orientations, different dendrite spacings will result, and these subdendrites, which are parallel to the original 71 dendrites, will always find new dendrites that are staggered by each other and grow into deeper layers of the eliminated grains, making the interface New migrations have taken place, thus maintaining the general trend of wide-spread interface advancement.

Therefore, high-temperature alloy single crystals can be made because they occupy 7 favorable dendritic relative positions. The rapid growth of small germanium crystals depends on the degree of inhibition of the other party's dendrite types and the sub-crystal 4 heat flow direction of the small sundries. The secondary dendrites grow longer than the secondary dendrites, so the suppression of the opposite branch by the secondary branch can achieve a faster rate of undershoot. Summarizing the knot of é—½25, we can know that the smaller the angle between the small miscellaneous dendrites and the heat flow direction, the smaller the miscellaneous crystals can obtain faster crystal growth rates in the A-line hot flow hall, and promote the elimination process of butadiene grains. Thus, it is a little miscellaneous; the speed of the person is faster. In the same way, the migration of the grain boundary of the microhybrid crystal has a nonlinear characteristic.

4 Conclusions The high-temperature production of single crystals in gold crystals, the key factor of the product and the expected single crystal of the relative spatial position of the branches, rather than Yuci-like growth of crystal-like growth direction is 4 parallel heat flow direction.

The use of secondary dendrite to inhibit the opposite party than the secondary dendrites can obtain 4 faster grain boundary migration speed.

The smaller the angle of preferred crystal orientation of the secondary dendrites and the direction of heat flow, the greater the migration rate of the emerging grains.

Grain interface migration has a nonlinear characteristic.

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