Search results

However, they did not identify the effects of grain refinement and dispersoids on the oxidation of alloys with ultra-fine grains.
The Ni-20Cr-20Fe-5Nb-1Y2O3 alloys with smaller grains and larger grains, Ni-20Cr-20Fe-5Nb, commercial Inconel 718 and PM1000 alloys were oxidized at 1000℃ for up to 100 hours.
The grain size of the Ni-20Cr-20Fe-5Nb-1Y2O3 alloy after grain growth heat treatment was 490nm.
Considering that the oxidation resistance of the Ni-20Cr-20Fe-5Nb-1Y2O3 alloy with a large grain size of 490nm was far superior to that of the Ni-20Cr-20Fe-5Nb alloy with a grain size of 128nm, it is believed that the oxidation resistance depends mainly on the addition of dispersoids rather than on the grain size(Fig.3).
The large number of Cr carbide particles formed in the boundary area in the alloy prior to oxidation are believed to form CDZ(carbide denuded zone), which has a lower Cr concentration than the matrix.

The TiNi alloy was exposed to HPT in the new die-set at a pressure of 6 GPa, and the number of rotations was n = 5.
(1) where r - the distance from the specimen axis, n - the number of rotations, h - the final height of the sample.
An average grain size after annealing at 400°С (1 h) was 20 nm as well; thus, there was no noticeable grain growth after a one-hour annealing.
The grains are equiaxed and possess sharply defined boundaries.
Annealing at a temperature of 550°С (1 h) leads to more intense grain growth and formation of a structure with the mean grain size of about 300 nm (Fig. 2 d).

The influence of the grain material, grain volume VG, grain size according to FEPA, axial feed faA, number of starts z0A and cutting speed vcA can be seen in Fig. 4.
The number of starts has the third biggest impact with approximately 15%, followed by grain material and grain volume with 10% and 7%.
The effect size of the number of starts and the grain material is clearly influenced by interactions with other parameters.
In the analogy trial each grain machines the same volume, but the number of cuts and the undeformed chip geometry are different.
The transferability of the influence of the number of starts to generating gear grinding is therefore not directly possible, because depending on the number of starts z0 during generating gear grinding the number of grains which are used for grinding a tooth gap varies.

It is believed that the increase of the transmittance after HIPing was attributed to the growth of the grain size and the reduction of the number of grain boundaries and pores.
As figure 2 shows, after hot pressing, the grain size is small and not uniform, mainly ranging from 2 to 5µm or from 10 to 20µm, and there are many grain boundaries.
After HIPing, the grain size increased obviously and became uniform, ranging from 50 to 100µm, the grain boundary area decreased, and no pores can be observed.
Therefore, the scatter due to grain boundaries and pores decreased.
Both before and after HIPing, the fracture occurred mainly along the grain boundaries, HIPing treatment increased the grain size and decreased the number of grain boundaries but did not change the fracture mechanism.

If the thermal expansion coefficients and elastic modulus of Ni base alloy and ceramic grain are different, there will be thermal stresses between grain and matrix in thermosyphon.
Ni base alloy ceramic composite coating is a mechanic disordered composite [2], a large number of ceramic grains are distributed in ductile matrix.
Because the thermal expansion coefficients and elastic modulus of Ni base alloy and ceramic grains are different, there will be thermal stresses in both grains and matrix in thermosyphon process.
The volume fraction of ceramic grains is f.
We can have the average stress in ceramic grain by the same method

A large number of defective grain boundaries (GBs) existing in NC materials may act as "short-circuit" diffusion channels, so that atomic diffusion in NS materials is expected to be much enhanced relative to their coarse-grained counterparts.
Kolobov et al [6] noticed diffusivities of Cu in a NS Ni (with a grain size of about 300 nm, synthesized by means of severe plastic deformation) are about 4~5 orders of magnitude higher than those in the coarse-grained Ni.
Its basic principle is the generation of plastic deformation in the surface layer of a bulk material by means of a large number of repeated multidirectional impacts of flying balls onto the sample surface over a short period of time, resulting in a progressive refinement of coarse grains into the nanometer regime.
Actually, when the grain sizes are smaller than a critical value, dislocations will hardly be piled up in grains and the nanocrystallites become dislocation free [20].
The grain size can be refined to such a fine scale and with high diffusivity.

The Aero-thermodynamic Effect Simulation Study of Solid Motor Grain Wen-geng PAN1,a, Tao LI 1,b, Guang-rong BIAN1 and Jin-rong CAO1 1Department of Aviation Ammunition, Air Force Logistics College, Jiangsu Xuzhou 221000, China anjlgdx2007@sina.com, bjiangnanlt@sina.com Keywords: missile, solid motor grain, aerodynamic heating, temperature field.
For high-speed flight's missile, thermal coefficient of expansion between the different structural and element will be different simultaneously, when the aerodynamic heating will produce, the grain and the thermal insulation layer will also be appeared the crack phenomenon in the influence of expand with heat and contract with cold rules.
Visible, it is not that the lesser number of the crack on the propellant column the smaller influence for the solid rocket motor, as long as the main crack and auxiliary crack arranged in a certain way, it is possible to reduce the harm of the crack to the propellant column.
Research of The Solid Propellant Grain Structural Integrity under Temperature and Pressure Loads.
HongDu Science And Technology, 2005 (1) [3] Wei Zhongwei, Xiao Jun, Liu Jianjie, Thermal Stress Failure on Heat Insulation Coatings for Airborne Missile Fuselage Connection, Aero Weaponry, 2006 (4) 50-52,59 [4] Liu Zhuqing, Yan Shidong, Ding Biao, Effect of Grain Crack to Solid Rocket Motor Performance, Journal of naval aeronautical engineering institute, 2007 (4) : 443 -444.

Twins structure formed in the previous annealing treatment could be seen clearly located in some grains.
All the grains are separated by straight boundaries.
The grain boundaries changed their shape to curve.
Fig. 2a describes the change of crater number, i.e. area density.
The non-stationary stress fields lead to the severe deformation of grains in the modified surface.

Synopsis of the literature on fatigue of nanostructured and ultrafine grain materials An analysis of journal articles and conference proceedings listed in ISI SciSearch®, ISI Proceedings®, and the Engineering Index® since 1990 shows that there has been a steady increase in the number of publications on fatigue in nanocrystalline or ultrafine grain materials.
Fig. 1 shows the increasing rate of growth in the cumulative number of publications on fatigue of this class of materials from zero in 1990 to 498 today.
Having a combination of large and small grains presumably offers both the effects of higher strength associated with the smaller grains and the enhanced ductility associated with larger grains.
The total number of fatigue cycles to failure at a constant applied cyclic stress during totalN can be partitioned into three stages: growth link incub total NNNN --?
where incubN is the number of loading cycles to incubate an initial crack, linkN is the number of additional cycles extend this crack through the short crack behavior stage via additional nanovoid nucleation and linkage, and growthN is the number of cycles to propagate the crack to failure.

A number of SPD techniques have been developed up to now.
For grain the tolerance angle was less than 15˚.
The grain size distribution is wide (from 1.4 to 56 µm) with average grain size of 5.6 µm.
Grains are heavily dislocated.
Ni/N is number fraction of grain boundaries with misorientation in the interval Analysis of the dependencies of microhardness, microstress, grain and subgrain sizes on annealing temperature reveals significant contribution of internal stresses to the strengthening of Mo by MF due to high dislocation density in the core of grains and to non-equilibrium state of grain boundaries [13].