外文翻譯--通過注射成型制造壓電陶瓷聚合物復(fù)合材料（英文）

1、FABRICATION OF PIEZOELECTRIC CERAMlClPOLYMER COMPOSITES BY INJECTION MOLDING. Leslie J. Bowen and Kenneth W. French, Materials Systems Inc. 53 Hillcrest Road, Concord, MA 01742 Abstract Research at the Materials Resea

2、rch Laboratory, Pennsylvania State University has demonstrated the potential for improving hydrophone performance using piezoelectric ceramic/polymer composites. As part of an ONR-funded initiative to develop cost-

3、effective manufacturing technology for these composites, Materials Systems is pursuing an injection molding ceramic fabrication approach. This paper briefly overviews key features of the ceramic injection mold

4、ing process, then describes the approach and methodology being used to fabricate PZT ceramic/polymer composites. Properties and applications of injection molded PZT ceramics are compared with conventionally pr

5、ocessed material. Introduction Piezoelectric ceramic/polymer composites offer design versatility and performance advantages over both single phase ceramic and polymer piezoelectric materials in both sensing and actua

6、ting applications. These composites have found use in high resolution medical ultrasound as well as developmental Navy applications. Many composite configurations have been constructed and evaluated on a laboratory

7、 scale over the past thirteen years. One of the most successful combinations, designated 1-3 composite in Newnham’s notation [l 1, has a one-dimensionally connected ceramic phase (PZT fibers) contained within a

8、three-dimensionally connected organic polymer phase. Hydrophone figures of merit for this composite can be made over 10,000 times greater than those of solid PZT ceramic by appropriately selecting the phase charac

9、teristics and composite structure. The Penn State composites were fabricated [ l ] by hand-aligning extruded PZT ceramic rods in a jig and encapsulating in epoxy resin, followed by slicing to the appropriate thicknes

10、s and poling the ceramic. Aside from demonstrating the performance advantages of this material, the Penn State work highlighted the difficulties involved in fabricating 1-3 composites on a large scale, or even

11、 for prototype purposes. These are: 11 The requirement to align and support large numbers of PZT fibers during encapsulation by the polymer. 2) The high incidence of dielectric breakdown during poling arising from the

12、 significant probability of encountering one or more defective fibers in a typical large array. Over the past five years several attempts have been made to simplify the assembly process for 1-3 transducers with the

13、 intention of improving manufacturing viability and lowering the material cost. Early attempts involved dicing solid blocks of PZT ceramic into the desired configuration and back-filling the spaces with a polymer

14、phase. This technique has found wide acceptance in the medical ultrasound industry for manufacturing high frequency transducers [2]. More recently, Fiber Materials Corp. has demonstrated the applicability

15、of its weaving technology for fiber-reinforced composites to the assembly of piezoelectric composites [31. Another exploratory technique involves replicating porous fabrics having the appropriate connectiv

16、ity [41. For extremely fine scale composites, fibers having diameters in the order of 25 to 100 pn and aspect ratios in excess of five are required to meet device performance objectives. As a result, these diffi

17、culties are compounded by the additional challenge of forming and handling extremely fine fibers in large quantities without defects. Recently, researchers at Siemens Corp. have shown that very fine scale composi

18、tes can be produced by a fugitive mold technique. However, this method requires fabricating a new mold for every part [51. This paper describes a new approach to piezoelectric composite fabrication, viz:

19、 Ceramic injection molding. Ceramic injection molding is a cost- effective fabrication approach for both Navy piezoelectric ceramic/polymer composites and for the fabrication of ultrafine scale piezoelectric com

20、posites, such as those required for high frequency medical ultrasound and nondestructive evaluation. The injection molding process overcomes the difficulty of assembling oriented ceramic fibers into composit

21、e transducers by net-shape preforming ceramic fiber arrays. Aside from this advantage, the process makes possible the construction of composite transducers having more complex ceramic element geometries than thos

22、e previously envisioned, leading to greater design flexibility for improved acoustic impedance matching and lateral mode cancellation. Process Descriotion Injection molding is widely used in the plastics industry as a

23、 means for rapid mass production of complex shapes at low cost. Its application to ceramics has been most successful for small cross- section shapes, e.g. thread guides, and large, complex shapes which do not requir

24、e sintering to high density, such as turbine blade casting inserts. More recently, the process has been investigated as a production technology for heat-engine turbine components [6,71. The injection molding process

25、used for PZT molding is shown schematically in Figure 1. By injecting a hot thermoplastic mixture of ceramic powder and organic binder into a cooled mold, complex shapes can be formed with the ease and rapidity nor

26、mally associated with plastics molding. Precautions, such as hard-facing the metal contact surfaces, are important to minimize metallic contamination from the compounding and molding machinery. For ceramics, the

27、 binder must be removed nondestructively, necessitating high solids loading, careful control of the binder removal Figure 3 shows green ceramic preforms fabricated using this tool configuration. Note that all o

28、f the PZT elements ejected intact after molding, including those having no longitudinal tapering to facilitate ejection. Slow heating in air has been found to be a suitable method for organic binder removal. Fin

29、ally, the burned-out preforms are sintered in a PbO- rich atmosphere to 97-98% of the theoretical density. No problems have been encountered with controlling the weight loss during sintering of these composite prefo

30、rms, even for those fine-scale, high-surface area preforms which are intended for high frequency ultrasound. . .- . .. -. .. L. . Figure 4: Scanning Electron Micrographs of As-molded (Upper) and As-sintered (L

31、ower) Surfaces of PZT Fibers. Figure 4 illustrates the surfaces of as-molded and as-sintered fibers, showing the presence of shallow fold lines approximately 10pm wide, which are characteristic of the injection mo

32、lding process. The fibers exhibit minor grooving along their length due to ejection from the tool. Figure 5 shows the capability of near net-shape molding for fabricating very fine scale preforms; PZT element dimensi

33、ons only 30pm wide have been demonstrated. The as-sintered surface of these elements indicates that the PZT ceramic microstructure is dense and uniform, consisting of equiaxed grains 2-3pm in diameter. Figure 5

34、: Fine-scale 2-2 Composite formed by Near Net- shape Molding (Upper Micrograph). As-sintered Surface (Lower Micrograph). In order to demonstrate the lay-up approach for composite fabrication, composites of approximate

35、ly 10 volume percent PZT-5H“ fibers and Spurrs epoxy resin were fabricated by epoxy encapsulating laid-up pairs of injection molded and sintered fiber rows followed by grinding away the PZT ceramic stock used to mold

36、 the composite preform. Figure 6 shows composite samples made from freshly-compounded PZT/binder mixture and from reused material. Recycling of the compounded and molded material appears to be entirely feasible and

37、 results in greatly enhanced material utilization. Table 1 compares the piezoelectric and dielectric properties of injection molded PZT ceramic specimens with those reported for pressed PZT-5H samples prepared by t

38、he powder manufacturer. When the sintering conditions are optimized for the PZT-5H formulation, the piezoelectric and dielectric properties are comparable for both materials. Since the donor- doped PZT-5H form

39、ulation is expected to be particularly sensitive to iron contamination from the injection molding equipment, the implication of these measurements is that such contamination is negligible in this injection m