engineering and in situ intrinsically processing of boron-based, carbon

ENGINEERING AND IN SITU INTRINSICALLY PROCESSING OF BORON-BASED, CARBON NANO FIBER REINFORCEMENT IN A HYBRID COMPOSITE IMPLANT 1

BAKR M. RABEEH, 2MAHMOUD M. ABU-ELKHAIR, 3MAHMOUD H. REDA 1

Prof. of Engineering and Materials Science, German University in Cairo, GUC. Egypt. Email: [email protected] 2,3 UG Student, Engineering And Materials Science Dept., GUC, Egypt. Email: [email protected], 3 [email protected]

Abstract: The need for more efficient and faster wound healing and bone regeneration is advancing on daily basis, whether it is for sports related injuries or for soldiers on the battlefield. Combination of such exceptional properties in one class of material is rare, but is urgently needed to meet the increasingly more demanding and multifunctional needs that advanced engineering systems have. The aim of this research is to introduce new and improved materials for wound healing and bone regeneration. Boron-based carbon fibers are engineered with a hybrid composite implant via nontraditional in situ direct metal oxidation, DIMOX, processing with the synergetic effect of alloying elements and semisolid interaction Rheocasting, Thixocasting and Powder Pack. Boron-based inorganic fibrous solids have been synthesis via the addition of 5 wt. % boric acid to the recycled aluminum alloy (Al-Si-Mg) at 1150oC for 20 minute, then Rheocasted at 750oC for 20 minutes. The product is then Rheocasted in a 5:4 wt. % melted mixture of borax and boric acid at 550oC for 20 minutes. The application of Rheocasting technique along with DIMOX, and semisolid Thixocasting have confirmed the objective of introducing fibrous coating and impregnated of boron based carbon enriched fibers in alumina/aluminum matrix in Nano and micro scale. Microstructural and mechanical characterization established applying scanning electron microscopy, SEM, energy dispersive X-ray spectroscopy, EDX and 3-point bending testing. The results provide an overview of recent needs in boron/carbon coating structures that are very effective in wound healing and bone regeneration. Orthopedic hybrid composite implant coated and impregnated with borate glass for diabetic patients are its wide spectrum applications. Bioactive amorphous and crystalline form of boron/carbon bulk and Nano fibrous coating/ impregnated is intrinsically synthesis for multifunctional hybrid composite materials. Keywords: Coating, Diabetic Patients, Heat Resistant, Hybrid Composite, Implants, Orthopedic, Porous Composite

matrix and with clean interfaces between ingredient sand matrixes. MMCs are generally processed with solid state processing (hot unidirectional pressing and hot isostatic pressing), and liquid metal routes (stir casting and infiltration). However, A direct metal oxidation, DIMOX, route is also used for specific applications [7]. This work aimed at the synergetic effect of the application of nontraditional processes; DIMOX along with rheocasting and infiltration technique. One of the problems associated with the infiltration route is the high volume fraction of the reinforcement which requires additional processes to dilute the content to the required levels. Prolonged processing times and increased processing steps at elevated temperatures aid the chemical reactions between matrix and reinforcements, which often result in brittle secondary phases [8]. Metal matrix composites (MMCs) are one of the important innovations in the development of advanced materials. Among the various matrix materials available, aluminum and its alloys are widely used in the fabrication of MMCs and have reached the industrial production stage. The emphasis has been given on developing affordable Al-based MMCs with various hard and soft reinforcements (SiC, Al2O3, borosilicate, and others delocalized zone of interests) because of the likely possibilities of these combinations in forming highly desirable composites

I. INTRODUCTION Demand for developing metal matrix composites for use in high performance applications; have significantly increased in the recent times. Among these composites, aluminum alloy matrix composites attract much attention due to their lightness, high thermal conductivity, moderate casting temperature and others. Various kinds of ceramic materials, e.g. SiC, Al2O3, MgO and B4C are extensively used to reinforce aluminum alloy matrices [1-3]. Boron, based structural materials can provide mechanically strong, thermally stable, structural materials with effective radiation shielding for different fields of application. These are; aeronautics (military and civil), astronautics, automotive and biomedical engineering [4-5]. The objective is to introduce boron based carbon fiber into aluminum matrix composite. The control of reinforcement shape, size and composition is established via the selection of nontraditional methods. One of the major challenges when processing MMCs is achieving a homogeneous distribution of reinforcement in the matrix as it has a strong impact on the properties and the quality of the material [6]. To obtain a specific mechanical/physical property, ideally, the MMC should consist of fine fibers/whiskers distributed uniformly in a ductile

Proceedings of 77th The IRES International Conference, New York, USA, 15th-16th August 2017 13

Engineering and in Situ Intrinsically Processing of Boron-Based, Carbon Nano Fiber Reinforcement in a Hybrid Composite Implant

[9]. Borate glass, in the form of fibers or particulates, has long been recognized as a high-strength, lowdensity material. Aluminum borosilicate fibers/particulate MMCs produced by solidification techniques represent a class of inexpensive tailormade materials for a variety of engineering applications such as aerospace components, Functionally graded materials, [10], bushes, and bearings [11]. Their uses are being explored in view of their superior technological properties such as the low coefficient of friction [7], low wear rate [12], superior gall resistance [8] and high thermal limitations [13]. This has led to increases research interest on evaluating the effect of type and weight fraction of reinforcement in the matrix and procedure that used to produce of MMCs [14-16]. In addition a need to introduce structural composite foam materials [17].

Table1: Table 1. Chemical composition (wt. %) of the Al-alloy used in the study. Cu Mg Si Fe Mn Ni 3.37 1.13 8.54 1.20 0.19 0.04 Zn Pb Sn Ti Al 1.36 0.07 0.03 0.04 Bala nce 2.2. Experimental Procedure The metal matrix composite used in the present work was carried out either by the direct metal oxidation method, DIMOX, or DIMOX with Rheocasting or DIMOX and Rheocasting with infiltration technique. The aluminum metal (scrap) was melted to the desired DIMOX temperature of 1150oC in alumina crucibles with addition of 5 wt. % boric acid. The melt was hold in the furnace for a prescribed holding time of 20 minutes. A three-phase electrical resistance furnace with temperature controlling device was used for melting. For each melting 300 400 g of alloy was used. The DIMOX molten metal was then poured in a metallic mold. For the purpose of comparison, the DIMOX samples were applied to non-traditional semisolid reaction, Rheocasting at 750oC for 20 minute then normalized cooling. In addition, infiltration technique is introduced for the DIMOX solidified samples. The DIMOX samples, with 5 wt. % boric acid additions, were then dipped in molten mixture of borax and boric acid (5:4 wt. % respectively) at temperatures of 550oC separately for 20, and 30 minute holding time (Powder Pack). The melting was carried in a tilting electric furnace in a range of 1150 ± 10oC.

Two different systematic approaches are utilized either by alloying elements effects or by applying new nontraditional infiltration process. Direct metal oxidation, DIMOX, is applied to recycled aluminum alloy, Al-Si-Mg, at 1150 oC for 20 minutes. The effect of alloying elements addition is applied at 1100oC for 2, 5, 10, 20, and 25 wt. % of boric acid powder for 20 minutes. The solubility limit along with alloy segregation is established via the application of semi-solid process; Rheocasting at 750oC for 20 minute. The application of pressureless infiltration technique is introduced for the synthesis and processing of low cost, light weight, uniformly distributed fiber, particulate hybrid orthopedic composite. The control of reinforcements shape and size along with its uniformity are obtained. Constituents’ agglomeration as well as its nonuniformity is achieved via infiltration. New carbon rich borosilicate fiber in bulk and Nano scale is achieved.

III. RESULTS AND DISCUSSION Micro structural studies were conducted in order to investigate the distribution of composite constituents intrinsically retained in the residual aluminum metal matrix. Samples were taken to reveal the micro constituents distribution on a microscopic scale. Micro structural characterization studies were conducted on DIMOX, DIMOX with Rheocasting technique, and DIMOX with infiltration technique. Parametric study with the synergetic effects of alloying elements (borax and boric acid) are introduced to control composite constituents in a uniformly distributed shape.

II. DETAILS EXPERIMENTAL 2.1. Materials The matrix material used in the experimental investigation was an aluminum alloy (Si –8.54%, Mg – 1.13 %), whose chemical composition is listed in Table-1. This alloy is mainly used when good mechanical properties are required. It is, in practice, a general-purpose high strength casting alloy. In its heat-treated form, its tensile strength can be increased from around 130-150 N/mm2 to up to 230-280 N/mm2. Aluminum and silicon alloys have no solidsolubility below the eutectic, and the microstructure solidifies in the form of silicon particles in an aluminum matrix. Aluminum-silicon castings have good corrosion resistance and are used in the cases where particularly high strength is required.

The composite samples were metallographically polished prior to examination. Characterization was done in etched conditions. Figure 1 a, b and c presents microstructure characterizations of the DIMOX samples compared with DIMOX with Rheocasting samples. Figure 1 a presents the uniformity of composite constituents along bulk surface that conducted with DIMOX only. In the contrast, Figures 1b and c present composite constituents ingredients more dominant with



agglomeration and delocalized coarse intermetallic whiskers and bulk fibrous carbon at DIMOX and Rheocasting technique at 750oC for 30 minute. Figure 1c presents high magnification bulk carbon fibers delocalized at DIMOX and Rheocasting.

presented in Table 2. The DIMOX structure with boric acid addition introduced with non-uniformity of composite structure along its central axis. The segregation of alloying elements induces hybrid composite structure with different composite ingredients.

Metallographic samples were sectioned from the cast bars. A 0.5 % HF solution was used to etch the samples wherever required. To see the difference in distribution of fiber/whiskers in the aluminum matrix microstructure of samples; first group of sample was prepared with DIMOX at 1100oC for 20 minutes with different addition of boric acid (from 2 to 25 wt. %), and the second group of sample has been fabricated with the addition of infiltration technique just after DIMOX at 1150oC for 20 minute of 5 wt. % only. The two groups were developed via the recycling of aluminum alloy, Al-Si-Mg scrap. The objective of this work is to monitor the effect of infiltration technique as a new nontraditional process that induces either surface or bulk fibrous/whiskers structure reinforced aluminum alloy. Agglomeration and non-uniformity of composite constituents were dominant when applying DIMOX. Fig.2a and b present SEM of DIMOX sample at 1150oC for 20 minutes with (a) 2% boric acid, and (b) 5 % boric acid. Porous matrix is obtained with intermetallic fibrous (Fig. 2 a), while with increase the percentage to 5 % new phase in Nano fibrous state dissolved within the matrix (Fig. 2b).

Figure 12 to Figure 18 present the obtained scanning electron microscopy and EDX for the second group of samples that DIMOX with infiltration pressureless technique. Figure 12 and Figure 13 presents scanning electron microscopy of DIMOX sample at 1150oC and 5 % boric acid and infiltration at 550oC for 20 minute, with uniformly distributed surface ingredients at low mag. and high mag. respectively. New hybrid composite morphology is obtained with new fibrous coating and uniformly distributed Widmanstatun structure. Figure 14 presents scanning electron microscopy of DIMOX sample at 1150oC and 5 % boric acid and infiltration at 550oC for 20 minute, with minor coating and loose fiber (at sample center) with low magnification. The outer surface of the sample reveals bulk coating fibers that presented in Figure 12 and 13. While Figure 14 and Figure 15 present two different types of fibrous structure 10 m and 1 m fiber diameter thickness. EDX is conducted to resolve the three types of fibrous structure those being obtained and analyzed at Figure 16, 17 and 18 for dispersed fiber, embedded fiber and coating fiber respectively. Figure 19 and 20 present SEM and EDX spots of a sample DIMOX and infiltration technique (30 minute) for coated fibrous structure low magnification, and high magnification respectively. The final chemical compositions of the three delocalized zone of interest 1, 2 and 3 are detected and concluded in table 3. Borosilicate fibers in a bulk as well as in Nano scale are introduced as coating as well as dispersed fibers. Boron content is dominant at the three types of delocalized zone of interest, boron enriched (1), bulk matrix (2) coated fibers (3) are recommended for biomedical engineering applications. Mechanical characterization established via 3-point bending test for the three samples (as received, DIMOX at 1150oC and DIMOX + infiltration at 550oC) and presented in Figure 21.

The segregation of alloying elements along with the increase of boric acid percentage induce borate glass fibers with intermetallic whiskers that presented in Figure 3 a (at 20% boric acid). And Figure 3 b (at 25 % boric acid) presents more alloying elements segregation that induces bulk fibers of borate glass and bulk grain enriched with Si that presented in Figure 3 b. Figure 4 presents scanning electron microscopy of DIMOX sample at 1150oC and 5 % boric acid with delocalized bulk whiskers agglomeration at sample center. Non-uniformity and delocalized composite ingredients were obtained as massive whiskers (5-350 m). Figure 5 presents scanning electron microscopy of DIMOX sample at 1150oC and 5 % boric acid with delocalized bulk randomly distributed fibers at sample surface (low mag.). Three different composite constituents were monitored at the surface of the sample as; short fibers (A), fine particulates (B) and bulk coarse particulates (C) and presented in Figure 6. Faceted structure is the character of grain boundaries as well as bulk whiskers that presented at Figure 7 and Figure 8 for high magnification. Energy dispersive X-ray spectroscopy is conducted at the three different composite constituents A, B and C and presented in Figure 9 to Figure 11 respectively. The EDX analysis is summarized by Chemical composition of delocalized zone of interests, fiber (A), fine particulates (B), and bulk/coarse particulates (C) and

(a)



(b)

(b)

Fig.3.SEM of DIMOX sample at 1150oC for 20 minutes with (a) 20% boric acid, (b) 25 % boric acid.

(c)

Fig. 4. Scanning electron microscopy of DIMOX sample at 1150oC and 5 % boric acid with delocalized bulk whiskers agglomeration at sample center [low mag.]

Fig. 1.Microstructure examination of DIMOX at 1150oC for 20 minutes (a) with, with 5% boric acid, (b) and (c) DIMOX with 5 % boric acid and Rheocasting at 750oC for 20 and 30 minute.

(a)

Fig.5.SEM of DIMOX sample at 1150oC and 5 % boric acid with delocalized bulk randomly distributed fibers at sample surface [low mag.]

,

Fig. 6.SEM of DIMOX sample at 1150oC with 5 % boric acid and three marked zone for EDX, a; fiber, b; fine particulate and c; coarse particulates.

(b) Fig.2.SEM of DIMOX sample at 1150oC for 20 minutes with (a) 2% boric acid, (b) 5 % boric acid.

Fig.7.SEM of DIMOX sample at 1150oC with 5 % boric acid and bulk particulate [low mag.]

(a)



Fig.12.Scanning electron microscopy of DIMOX sample at 1150oC and 5 % boric acid and infiltration at 550oC, with uniformly distributed ingredients [low mag.]

Fig.8.SEM of DIMOX sample at 1150oC with 5 % boric acid and bulk whisker twining [high mag.]

Fig.9.Energy dispersive x-ray spectroscopy of marked A zone [fiber structure, fig. 6]

Fig.13.Scanning electron microscopy of DIMOX sample at 1150oC and 5 % boric acid and infiltration at 550oC, with uniformly distributed ingredients and coating layer [high mag.]

Fig.10.Energy dispersive x-ray spectroscopy of marked B zone [particulate structure, fig. 6 Fig.14.Scanning electron microscopy of DIMOX sample at 1150oC and 5 % boric acid and infiltration at 550oC, with minor coating fiber [high mag.]

Fig.11.Energy dispersive x-ray spectroscopy of marked C zone [bulk whisker structure. Table 2. Chemical composition of delocalized zone of interests, fiber (A), particulates (B), and bulk whiskers (C) Element

Zone A

B C O Mg Al Si Fe Total

0.75 2.26 74.15 22.83 100

Zone B Wt. % 90.37 9.63 100

Fig.15. Scanning electron microscopy of embedded fibers and bulk fibers [v. high mag.]

Zone C 3.15 2.88 61.51 11.21 21.25 100

Fig. 16.EDX of a sample DIMOX and infiltration technique for a dispersed fibrous structure.



Fig.17.EDX of a sample DIMOX and infiltration technique for an embedded fibrous structure.

Fig.21. 3-point bending stress strain diagram of the three samples as received, DIMOX at 1150oC and DIMOX with infiltration at 550oC. Fig.18.EDX of a sample DIMOX and infiltration technique for coated fibrous structure.

CONCLUSIONS DIMOX with the addition of boric acid is introduced with new nontraditional hybrid composite structure with fibrous and particulates. Effect of temperature at 1150oC is more dominant of introducing a new hybrid composite only at 5 wt. % addition of boric acid instead of 25% addition. The non-uniformity and agglomeration of composite constituents is dominant along surface and through sample center. Rheocasting at 750oC after DIMOX at 1150oC induces new nontraditional boron-based carbon fibers. The addition of infiltration technique directly after DIMOX at 550oC for 20 minutes holding time introduced with its structural effect. The control of ingredients shape and size and its delocalized zone is introduced with new nontraditional hybrid composite structure. The refinements of fibrous/whiskers with its uniformity is introduced with the control of boron contents along three types of fibers. Boron based carbon fibers coating in orthopedic implants are being introduced for bone repair or as scaffolds for cell-based bone tissue engineering. Boron maintains bones, joints, neurons and may reduce cancer risk. The control of boron content is strongly introduced via infiltration technique. Dispersed, embedded or coating fibers are three different boron based fibers obtained via infiltration technique. The agglomeration and non-uniformity of composite constituents that obtained via semisolid reaction, Rheocasting, are being controlled via infiltration technique. Boron based rich-carbon fibers are introduced as coating and/or intrinsically mechanically alloyed in a hybrid composite structure. Borate glass has the same boron content even with change processing. Boron based coating fiber has around 4.07 wt. % boron content with enriched carbon content. The capillary action of infiltration induces Nano/micro fibers of boron based at 1.37 wt. % of boron. The refinement and uniformity of

Fig.19 SEM and EDX spots of a sample DIMOX and infiltration technique for coated fibrous structure.

Fig.20. SEM of a sample DIMOX and infiltration technique for coated fibrous structure [high mag.]. Table 3. Chemical composition of delocalized zone of interests, dispersed boron (1), bulk matrix (2), and coating B-C fiber (3)

Element

Dispersed boron 1

B C O Na Mg Al Zn Total

31.40 03.68 08.08 01.26 12.55 41.24 01.79 100

Bulk matrix 2 Wt. % 04.05 03.18 25.17 03.00 06.38 54.89 03.33 100

Coating fiber 3 07.58 19.40 34.80 01.61 14.71 21.29 00.61 100.00



structure by infiltration induces higher mechanical properties.

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