| Combining ~vith a key project supported by the National Ke~?Program of 9 Live year Plan, a novel multi-layer spray deposition ~MLSD) equipment for large dimensions pipe blanks have been developed. Pipe blanks of FVSO812 alloy with dimensions of (I) 400 X 800 X 115mm (inner diameter X length X wall thickness) were J)repared by MLSD technology. Thermal history and microstructure characteristics of the pipe blanks were analyzed. Alloy pipes with high performance were produced by extrusion and spinning process. The main conclusions were drawn as following:(1)The preparation principle of pipe blank with large dimensions by MLSD and the processing regularities were researched and analyzed. In present process, the atomized droplets spraying flow scans reciprocally along the surface of pipe substrate and the blank is deposited layer by layer with the atomizer and substrate moving simultaneously. Thus the scanning range of the spraying flow is large and the internal of the successive deposition at the same point is long ,which leads to a high cooling rate of the deposit above 104K s? So MLSD is more proper for preparation of FVSO8I2 alloy pipe blanks with large dimensions. The mean atomized droplet size and its size distribution were influenced by the atomization process parameters. such as atomization gas pressure (P3, temperature of melt (I) and the diameter of melt flow (D). The spatial matter flow density in the atomization cone presents a bimodal distribution. At the deposition stage, matter density vertical to the scanning direction (MDS) presents an approximate Gauss distribution. The sticking efficiency of the atomized droplets spraying flow and deposit density decrease as the increasing of spray distance (z).(2)Based on an intensive analysis on the process, the needed pipe blanks with fine shape precision and excellent quality were prepared. The results show that, to obtain pipe blanks with flat surface, the atomizer should move evenly and its speed U satisfy such expression as U ~ Lu1 r5/ ~t where Lu is the turning speed of the substrate and r,,5 is the half-width of MDS. The optimum process parameters in present study are as following: U ~0.1m s4, Lu 60r miff? Pz1.OMPa, T=96() ~C, D~4.0mm, z180~-220mm0(3)A one-dimension model of heat flow analysis was established to analysis the cooling and solidification of atomized droplets with different size during the flying and after their deposition. The results show that the average cooling rates of the dropletsxx-ith thc sisc bctuyccn 0 to 220 ll m can reach above 1 X 10'Ii. s-l dufu1g thc fl\-ingdistancc bctween 0 to 2()0min. the cooljng rates of dIop1ets witi1 the mean size of 9()P m can obtain 3.3 X l()'lt. s l after theiI deposihon. The average cooling ratc of thcdeposited la\-er can reach above 10'K. s-'. So it can be concluded that the couljng rateduring MLSD is about 103tw 105K. s-', which is higher than that either in convenh<)l1alspra\' deposihon and or in atoforahon. The dricrostructures of the atomizcd poxt.derparticles xt'ith different size xt7ere tested. The results shou- that the grains about 1() to 2()P m and needle-shaped phase with the size between 2 to 5 ll m are prescnted in thcpowder particles above 220 ll m. But in the deposiL the grain slze is ouly between 20()to 500nm wlth sphetical parhcles Q -Al,,(Fe,V),Si about 20 to 60nm.(4) The influences of densdriahon process on the rhastructures and propertiesof the allo}-'s piPes have been investigated. Extruded and spun p1Pes xv~id1 fineperfOrmance have been produced. The results show that the boe dixnensions extrudedpipe wtth high performance can be rnanufactuxed within the capacaq of the availableextiuding apparatus wtth optimUm processing. The mechanical properhes ofas-extruded piPes are apparend3 higher than that of extruded bar b}' com,enhonalspra}' deposition. The mechandal properhes of the extruded piPes are llstcd asfUll<)\L,ing.25'C f o ..==3l0MPa, o,=391MPa, 6 =11.4'/O;350OC, O .,==178MPa, o,=185MPa, 6 =12.5?,o.When...
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