1 IntroduCtion p一iron disilieide 15 one of the eandidates in ther-rnoeleetrie materials.It 15 famous forlts high workingtemPerature(200一90()oC),nontoxieity and high oxida-tion resistanee<1一4>.p一iron disilieide based se而eon-dueting materials are also attractive as functionalma-terials for thennoeleetrie energy eonversion and sen-sors,due to their excePtional high Seebeek eoeffi-eients,low material and Processing Priees,environ-mental sustainability and unli而ted availability· Based on the theoretieal analysis,the key to im-prove the energy eonversion effieieney 15 to reduceboth thermal eonduetivity and eleetrieal resistance onthe deviee suri恤ce<5>.ft has been shown before,thatthe functional ProPerties of FesiZ are sensitively de-Pendent on the eoneentration and quality of grainboundaries 16>.Fine erystalline may imProve thetherrnoeleetric figure of merit by redueing the thermaleonductivity stronger than the eleetrical eonductivity· R即id solidifieation 15 a convenientw盯to tuneafine crystalline而erostrUcture<7>·Hot Pressing isaProPer method to eomPact the Powders to high densitywithin a shorter time and at a lower temPerature thanPressureless sintering Proeesses,50 that any signifi-eantgrain growth of the materials ean be avoided andfine grain strUctures ean be ensured· In the Present work,FesiZ based thennoeleetrieal-loys have been PrePared by melt sPinning and hotPressing.The而erostrUetures of the materials wereanalyzed with XRD and SEM.ZExPerimental Rapid solid饭ed Powders of iron一disilieide(FesiZ)based materials PrePared by melt sPinning<7>,duringwhieh the alloy melt was driPPed onto the edge ofachilled rolling molybdenum wheel With a high sPeed·The rapidly solidified Powders were dlreetiy hot uni-axially Pressed(HUP)in a graPhite die at 90()oC,75MPa for 30而n for samPle 1 and 990oC,75 MPafor 30而n for samPle 2 resPeetively.After the densitymeasurements,the HUP samPles were eut into Pieees.Some of the Pieces,together with some melt一sPunflakes(starting materials)were annealed at S000C for20 h.The annealed samPle 2 Pieees were na们ned sam-Ple 3.Both HUP and annealing Proeesses were ea币ed砧out under a vacuum of about 10-3Pa. Mierostnlctu化5 we化observed With a LEO 982SEM after Polishing and etehing.For the flakes andsamPlel,wet etehing was used:while for samPleZand samPle3,ion raPid etehing by a RES 100 RapidEtehing System,using argon ion beam was aPPlied toProduee a better eontrast of the comPlicated Phases.XRD analyses were also ea币ed out to identify thePhase e0InPositions.J. Univ. Sci TechnoLBeijil忿g,VoLll,Nd.I,Feb20043ResllltsanddiSC此Sion3.1 Mierostruetures of the raPidly solidified flakes Most of the raPldly solidified Powders are thinflakes with a thiekness less than 0.1 rn幻n.SEM Pie-tures of the surfaee show there are further finer grainstrUetures with a eharaeteristie size of about 100 nm ina flake(figurel).during the re一melting Proeess before melt sPinning,inwhieh tungsten was used as the arc eleetrode.The ex-istenee of WSiZ makes the而erostrUCtures of the sam-Ples more elear,sinee the WSiZ Partlcles are formedalong the grain bound幼es of the melt sPinning strUc-tures.Figure 4 shows the而eros加etures of the flakesannealed at 800OC for 20 h.ROm figure4(a),it seemsthat the”striPe,,struetures were”eoPied,,after an-nealing,though X.ray dlfl介aetion Pattems of figure3伪)show that the annealed fiakes eontain oalyp如ase and some amount of WSi2.High magnifieationobservation was earried out for those”grooves,,loeat-ed between the striPes,whieh 15 shown in figure4(b).The dark areas in figure4(b)are Pores eaused by thevolume ehange after Phase transforming.As eon-6n刀ed by figure3(b),those small brightP叭ieles dis-Persed in the grooves are the introdueed WSi2.Thesefine WSiZ Partieles with the diameter about 50 nm arelocated along grain bound硕es,and aet as boundarybarriers for the srain growth of p Phase during heattreatment.Thus the fine”striP,,strUetures were”eoP-ied”even after p Phase transfonnation.(b).a一Fesi:令E·Fesi一p一FesiZ▲WSiZ FigUre 1 nne sur
More summaries about the Microstructures of FeSi_2 based thermoelectric materials prepared by rapid solidification and hot pr