Potassium-Doped Tungsten Bulbs Basic Content of Reinforcement Theory

Potassium foam reinforcement theory of the basic content includes three interconnected parts, which are :

(1) Potassium bubble formation and control. Tungsten oxide is added in trace potassium silicate , aluminum chloride mixed aqueous solution with hydrogen reduced to metal powder , and then compacts , sintering billet . Billet to form a large number of non-uniform distribution of the doping hole φ0.1 ~ 0.4μm . Analysis confirmed that potassium at room temperature to solidify the doped ionic pore walls , and tungsten have a coherent relationship . In the following rotary forging temperature , cold drawing and heat treatment process, the potassium -doped hole is flattened , elongated form along the filament axis orientation distribution of the " K tubes " or " K -line ." The greater the deformation process , the greater the aspect ratio of potassium tube . When annealed tungsten , potassium pipe expansion due to vaporization of potassium ( K boiling point of about 760 ℃), the temperature rose further instability potassium tubular shape , a split of the ovule , a bunch of potassium ordered bubble columns. Potassium tube split ovule instability of the process can be seen as a cylinder instability and approximate equation with perturbation theory and its potassium bubble dispersion model to establish quantitative expression equation, namely the establishment of the aspect ratio of potassium tube and the degree of deformation relationship L / W = (0.75 ~ 1.3) (Do / Dk) 4, ( wherein L, W, Do, Dk namely potassium tube length , width, diameter and tungsten rod original diameter after processing ) , and after dispersion derived The basic parameters of potassium bubble columns : bubble diameter potassium , potassium -containing foam bubble column number and spacing between two adjacent bubbles . Electron microscopic observation and experiment results calculated as consistent with each other . Experimental results and long-term production practice have shown that the necessary amount of potassium- doped hole is to ensure that the basis of potassium bubble dispersion , it depends on the additive potassium -doped tungsten optimum content ; while potassium and potassium bubble pipe split orderly diffusion model can control the degree of deformation and heat treatment through the system to reach . This design -doped Si, Al, K , and a reasonable amount of added processing to develop a reasonable degree of deformation and heat treatment system provides a credible scientific basis .

( 2 ) Potassium soak in the process of recrystallization behavior and mechanism of action . Along with the wire axis parallel to the direction of the ordered arrangement of potassium -doped tungsten bulb is caused by recrystallization behavior -specific basis . General material at an appropriate temperature after recovery and recrystallization processes , the formation of equiaxed grains without deformity . However , at high temperature to form doped tungsten filament axis direction along the particular aspect grow large particles , even cross-section of the wire is covered with 1 to 2 grains . It is this special grain boundary growth and finger overlapping grains , the tungsten doped with excellent high-temperature creep resistance , or anti- sag properties of tungsten . Ordered along the filament axis parallel to the direction of the distribution of potassium bubble column, a high temperature high vapor pressure within the bubble to bubble K corresponds to the second phase particles , strong pinning the grain boundary ( see Figure 1 ) , So a aspect suppress recrystallization , improves the recrystallization starting temperature , on the other hand to hinder the grain boundary migration radial filaments , and force it to move the wire axis , thus forming a special aspect of great growing grains ( see Figure 2 ) . The potassium bubble behavior and grain growth model has been a large number of experimental observations and theoretical calculations confirmed, but the details of its recrystallization processes and mechanisms are still not fully unified understanding. The focus of disagreement reply , primary and secondary recrystallization phasing and specific growth or soaring mechanism . Most people think that the first stage of recrystallization primary recrystallization in deformed grains gradually formed simultaneously coarse wire axis parallel to the series as the main feature of potassium bubble , but some people think it is the processing state of the Asian crude fiber bundles crystal ( see sub-structures ) polymerization grew up belonging to a polygon or restoration process . It was also defined as the in-situ re -crystallization process, the formation of the rod or sub-grain ; recrystallization grains elongated second stage is called overgrowth rapid growth or even covered wire cross-section of the main feature. However, this process is defined as the primary or secondary recrystallization still significant differences. Chinese scholar and his research group left Tieyong learn various scholars in the analysis based on the results , after years of systematic experimental and theoretical analysis , published a series of papers presented doped tungsten recovery and recrystallization nucleation mechanisms and recrystallization growth mechanism . The basic conclusion is that : first, the tungsten -doped high-temperature annealing occurs when deformed grains ( or fibers ) change phenomenon , is to resume the process of a special organizational change , grain boundary dissociation , Asia fiber aggregation caused by not once again crystallization behavior ; Second, because potassium bubble column grain boundaries and dislocations movement and its direction is strong pinning effect , resulting in a sub- fiber polymerization process proceeds very slowly and can be extended to temperatures above 2000K ; Third , doping the formation of abnormal grain growth in tungsten seemingly secondary recrystallization soaring organization, but experimental observations and theoretical calculations show that it is not the primary recrystallization occurs in a small number of matrix grain growth resumed , nucleation of new grains crystal growth and annexation of a few large new small recrystallized grains , and several other processes occur almost simultaneously complex process , based on deformation energy storage, grain boundary energy as the driving force , at different stages driven results can not simply traditional defined as the secondary recrystallization process .

( 3 ) Potassium bubble dispersion strengthening mechanism . Enhanced in a variety of materials, methods, dispersion strengthened (DS) is a second- phase strengthening , strengthening effect depends on the second phase of its chemical and thermodynamic stability , the ideal shape , small size , enough quantity and good dispersion . As a second phase of potassium bubbles all the conditions with the above , plus the size of the bubble and the dispersion K mode is controlled , but also shows the superiority of potassium bubbles , it has been classified as a number of dispersion strengthened in a distinctive strengthening mechanism . The second phase dispersion strengthened explain theoretical model matrix lot more is Orowan (Orowan) mechanism . Potassium bubble second phase particles as a special addition to causing diffusion rate decreases , increase the recrystallization temperature and thermal processing generate stable fibrous tissue and dislocation structures such as these Orowan strengthening indirectly strengthening mechanism , it must also see enhanced potassium bubble specificity, namely Asian organizations strengthening mechanisms . Ordered along the filament axis direction of potassium bubble column in processing fibrous form a distinct crystal growth , it is only at very high temperatures to form a clear long fibrous crystals and is very stable, and because of having abnormal , extreme aspect ratio large crystal growth and finger -shaped lock lap crystalline , less grain boundaries , especially grain boundaries transverse (perpendicular to the force of the grain boundaries ) less weakened creep at high temperatures plays a major role in the grain boundary sliding , thereby significantly improved tungsten -doped high-temperature creep strength. Research shows that the larger the aspect ratio , strength increase , the more significant aspect doped tungsten wire , usually above 20 . Experiments also showed that potassium bubbles on dislocation pinning attract and the more general second phase particles more powerful , its processing formed dislocation structure on the high-temperature strengthening greater role .


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