Tugas Resume Metalurgi Fisik (Fernando Desfriandi Saragih G1C019046)

 

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Tugas 3 SYNOPSIS dan mencari video - Fernando Desfriandi Saragih G1C019046

                                           METALURGI FISIK

 

 

Di susun oleh:

 

 

Nama : Fernando Desfriandi Saragih

NPM : G1C019046

DosenPengampu : A. Sofwan FA, S.T.,M.Tech.,Ph.D

     Nurbaiti S.T., M.T

 

PRODI TEKNIK MESIN

FAKULTAS TEKNIK

UNIVERSITAS BENGKULU

2020

Synopsis 2.11

 

1.Metals are crystalline materials. Atoms in a crystal structure occupy positions in an arrangement, which is characterized by periodicity. The atomic arrangement is systematically repeated in three-dimensional space.

2. Atomic arrangement can be described with the aid of the unit cell. Its repetition in three directions generates the crystal structure.

 3. Atoms in metals are arranged in close-packed structures. The most important crystal structures of metals are base-centered cubic (BCC), face-centered cubic (FCC) and hexagonal close-packed (HCP). Structure of metals 39

 4. The crystal structure influences several phenomena in physical metallurgy such as the potential of a metal to form alloys, the plastic deformation of metals and diffusion, which is the transport of atoms through the lattice.

 5. Metals form two types of solid solutions: interstitial and substitutional solid solutions. The size of interstitial sites determines the maximum solid solubility in interstitial solid solutions. The formation of substitutional solid solutions is controlled by the Hume-Rothery rules. Most alloy systems do not fulfill these rules and, therefore, solid solutions exhibit a limited solid solubility.

 6. Intermetallic compounds form in most alloy systems. These compounds are either stoichiometric or exhibit a homogeneity composition range. The factors governing the formation, composition and crystal structure of intermetallic compounds include electronic structure, electronegativity, atomic radii of components and chemical bonding.

7. The microstructure of metals consists of the different phases (solid solutions and intermetallic compounds) and crystal imperfections including point defects (vacancies and interstitials), line defects (dislocations), grain boundaries and interfaces. The microstructure of a metal influences its properties. Microstructure can be altered through processing with the activation of phase transformations.

8. Thermodynamics defines the potential for a reaction or a transformation to take place while kinetics defines the rate of the reaction or transformation.

9. A system is said to be at a state of thermodynamic equilibrium when it is at mechanical, thermal and chemical equilibrium simultaneously. The criterion for thermodynamic equilibrium is the minimization of the Gibbs free energy. Any spontaneous transformation decreases the free energy of the system.

10. The reduction in free energy accompanying a transformation is the thermodynamic driving force of the transformation. The energy barrier, that should be surmounted in order for the transformation to take place, is the activation energy of the transformation.

11. The activation energy is defined by the Maxwell-Boltzmann energy distribution. The rate of a transformation is then exponentially dependent on activation energy and temperature via the Arrhenius law.

12. In a reaction or transformation consisting of several steps, the rate of the overall reaction is controlled by the slowest step, which exhibits the highest activation energy. This step is called the rate-limiting step.

Synopsis 3.5

 

1.Structural imperfections have a significant influence on physical and mechanical properties of metals. They can be classified as (a) point defects, such as vacancies and interstitials, (b) linear imperfections, such as edge and screw dislocations, (c) surface imperfections, such as grain boundaries and interfaces and (d) threedimensional defects, such as voids and inclusions.

2. At each temperature there exists a certain concentration of point defects at thermodynamic equilibrium in the crystal. The concentration of vacancies and interstitials increases exponentially with temperature, following Arrhenius-type temperature dependence. The concentration of interstitials is several orders of magnitude Structural imperfections 85 lower than the concentration of vacancies at the same temperature.

3. Vacancies play a key role in the diffusion of atoms, especially the substitutional diffusion.

4. Plastic deformation takes place by dislocation glide in specific slip planes (closepacked planes) and slip directions (close-packed directions), which constitute the slip systems of a metal.

5. A slip system becomes operational by the application of a certain stress on the slip plane, called the critical resolved shear stress (CRSS), which is directly related to the mechanical strength of the metal.

 6. The glide of an edge dislocation takes place in a direction parallel to the applied shear stress while the glide of a screw dislocation takes place in a direction perpendicular to the applied stress. In both cases the glide causes plastic deformation of the crystal.

7. At every position during glide, the dislocation line is the boundary between the part of the crystal that has slipped and the part which has not.

8. The stress required for dislocation glide is much lower than the ideal crystal strength. This explains the difference between the actual and ideal strength of a metal.

 9. The direction and magnitude of slip, caused by a dislocation, is expressed by the Burgers vector~b of the dislocation line. The Burgers vector is determined by the Burgers circuit.

10. The Burgers vector of an edge dislocation is perpendicular to the dislocation line. When this is valid for the entire dislocation line, then this is a pure edge dislocation. The Burgers vector of a screw dislocation is parallel to the dislocation line. When this is valid for the entire dislocation line, then it is a pure screw dislocation.

11. When a dislocation is not a pure edge neither a pure screw, it is a mixed dislocation. In this case the dislocation line forms a random angle with the Burgers vector.

12. Dislocations cannot terminate inside the crystal. They can terminate either at the crystal surface, at grain boundaries or on themselves, forming dislocation loops. The expansion of a dislocation loop under the action of a shear stress causes plastic deformation of the crystal.

 13. The elastic strain energy of a dislocation is associated with strains caused by the 86 Physical Metallurgy: Principles and Design displacement of atoms away from their equilibrium positions around the core of the dislocation line. The elastic strain energy is proportional to the square of the Burgers vector.

14. In several cases, the dissociation of a perfect dislocation into partial dislocations is energetically favored. The glide of these partials has the same effect as the glide of the perfect dislocation.

15. The dissociation of a perfect dislocation in FCC crystals into partial dislocations is accompanied by the formation of a stacking fault, characterized by the stacking fault energy (SFE). Despite the fact that the dissociation decreases the elastic strain energy of the crystal, if the Frank’s rule is obeyed, the dissociation will take place only if it decreases the total energy of the crystal.

16. In FCC metals with low SFE, slip takes place by the glide of partial dislocations, while in FCC metals with high SFE, slip takes place by the glide of perfect dislocations.

17. The change of slip plane by a screw dislocation is called cross slip. Cross slip of screw dislocations is important for the plastic deformation of metals, because it allows the dislocations to continue their glide in the crystal and produce plastic deformation.

18. The change of slip plane by an edge dislocation is called climb and requires the diffusion of vacancies or interstitials to the dislocation.

 19. Jogs and kinks are steps on the dislocation line. Jogs transfer a segment of the dislocation line to a different slip plane while kinks are steps on the same slip plane with the rest of the dislocation line. Kinks and jogs on an edge dislocation do not impede the glide of the dislocation. However jogs on a screw dislocation, impede its glide, since climb is required in order for the jogs to move with the dislocation.

20. The plastic strain rate resulting from dislocation glide is proportional to the mobile dislocation density and the average dislocation velocity.

21. The stress field around a screw dislocation is pure shear. The stress field around an edge dislocation involves shear on the slip plane as well as tension and compression below and above the slip plane respectively.

22. The energy of a dislocation is proportional to b 2 . The long-range stress field allows the dislocation to interact with point defects, solute atoms and other dislocations at long distances, up to 100b, from the dislocation core.

23. Regarding forces acting on dislocations: the glide force acts perpendicular to the Structural imperfections 87 dislocation line. The line tension acts to reduce the dislocation length. The bending force acts to bend the dislocation between obstacles. The stress required in order for a dislocation to bypass obstacles on the slip plane, in other words the resistance of the obstacles to dislocation glide, is inversely proportional to the distance between obstacles.

24. The major effects of dislocations are related to plastic deformation, strengthening and phase transformations. In the last case, dislocations enhance both the nucleation and growth of a new phase, by providing sites for the heterogeneous nucleation and by serving as high-diffusivity paths for the diffusional growth of the new phase.

 25. The primary interfaces in metals are the free surfaces, grain boundaries, interphase boundaries and stacking faults. All interfaces are characterized by an interfacial energy γ.

26. The surface energy of free surfaces is highly anisotropic. The equilibrium shape of a single crystal is the one that minimizes the total surface energy.

27. A grain boundary separates two regions of a crystal with the same crystal structure but with different lattice orientation. Grain boundaries are distinguished in tilt and twist boundaries as well as low-angle and high-angle boundaries.

 28. Interphase boundaries separate two different phases, which may have different crystal structure or chemical composition. Depending on whether there is full, partial or no coincidence of the two crystal lattices at the boundary, interphase boundaries are distinguished in coherent, semicoherent and incoherent boundaries.

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TUGAS PEKAN 2 (By Fernando Desfriandi Saragih G1C019046)

 

                                          METALURGI FISIK

 

 

Di susun oleh:

 

 

Nama : Fernando Desfriandi Saragih

NPM : G1C019046

DosenPengampu : A. Sofwan FA, S.T.,M.Tech.,Ph.D

     Nurbaiti S.T., M.T

 

PRODI TEKNIK MESIN

FAKULTAS TEKNIK

UNIVERSITAS BENGKULU

2020

  IKATAN ATOM

Bagian terkecil dari suatu materi baik gas, cairan maupun zat padat adalah atom. Atom-atom tersebut umumnya saling berinteraksi satu dengan yang lainnya akibat adanya gaya tarik menarik dan gaya tolak menolak antar sesamanya.

1. Ikatan ion

 

    Ikatan ion terjadi akibat adanya serah terima elektron sehingga membentuk ion positif dan ion negatif yang konfigurasi elektronnya sama dengan gas mulia. Ion positif dan ion negatif diikat oleh suatu gaya elektrostatik. Senyawa yang dihasilkan disebut senyawa ion.

        Sebagai contoh NaCl merupakan contoh senyawa ion yang sering kita jumpai di kehidupan sehari hari yang berupa garam. Dalam NaCl terdapat ikatan atom Na⁺Cl^- yang saling melakukan serah terima elektron untuk mencapai kestabilan sehingga disebut ikatan ion. 

 

Dari gambar diatas dapat dilihat bahwa :
   1. Na memiliki nomor atom 11 dengan konfigurasinya, Na = 2 8 1 dimana kulit terluarnya memiliki 1 atom.
   2. Cl memiliki nomor atom 17 dengan konfigurasinya, Cl = 2 8 7 dimana kulit terluarnya memiliki 7 atom.

2.Ikatan Kovalen

       Ikatan kovalen adalah ikatan yang terjadi akibat pemakaian pasangan elektron secara bersama-sama oleh dua atom. Ikatan kovalen terbentuk di antara dua atom yang sama-sama ingin menangkap elektron (sesama atom bukan logam).

          Pasangan elektron yang dipakai bersama disebut pasangan electron ikatan (PEI) dan pasangan elektron valensi yang tidak terlibat dalam pembentukan ikatan kovalen disebut pasangan elektron bebas (PEB). Ikatan kovalen umumnya terjadi antara atom-atom unsur nonlogam, bisa sejenis (contoh: H2, N2, O2, Cl2, F2, Br2, I2) dan berbeda jenis (contoh: H2O, CO2, dan lain-lain). Senyawa yang hanya mengandung ikatan kovalen disebut senyawa kovalen.

3.Ikatan Logam

   Ikatan logam adalah ikatan yang terjadi akibat gaya tarik menarik yang terjadi antara ion ion positif dengan elektron elektron pada kulit terluar dari suatu atom unsur logam .Ada juga teori yang menyatakan bahwa ikatan logam terjadi karena ada lautan elektron yang disebut teori awan elektron .

Menurut teori ini, Kristal logam tersusun atas ion-ion positif yang tidak bergerak dikelilingi oleh lautan elektron valensi yang bergerak  dalam kisi Kristal logam . Elektron-elektron valensu logam bergerak bebas dann mengisi ruang-ruang di antara kisi-kisi logam yang bermuatan positif .

Hubungan antara Energi ikatan atom dan Modulus Young 

Perhatikan gambar diatas :

• Terdapat atom ion yang memiliki r ( Jarak )
• Dari atom ion tersebut terbentuk 2 energi yaitu energi elektrostatik ( Tarikan ) dan energi repulsive (Tolakan)
•  Energi Elektrostatik, terjadi karena ada gaya tarik menarik antara atom yang dapat diperoleh dari Gaya Coulumb  

Dimana : 
Z = Valensi atom
e = Muatan elektron = 1,602 x 10^-19
ε = Permivitas ruang hampa = 8,85 x 10^-12 
r = Jarak antara atom

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TUGAS PEKAN 1 ,SPESIFIKASI KRISTAL (By Fernando Desfriandi Saragih G1C019046)

                                            

                                           METALURGI FISIK

 

 

Di susun oleh:

 

 

Nama : Fernando Desfriandi Saragih

NPM : G1C019046

DosenPengampu : A. Sofwan FA, S.T.,M.Tech.,Ph.D

     Nurbaiti S.T., M.T

 

PRODI TEKNIK MESIN

FAKULTAS TEKNIK

UNIVERSITAS BENGKULU

2020

 

SPESIFIKASI KRISTAL

NO	Spesifikasi Kristal	SC	BCC	FCC
1	Bilangan Koordinasi	6	8	12
2	Jarak Atom Terdekat	a	√3a/2	√2a/2
3	Konstantas Kisi(a)	4R	(4/3^1/2)R	(4/2^1/2)R
4	Banyak Atom Per sel satuan	1	2	4
5	Banyak titik kisi(yakni pusat bola)	8	9	14
6	Volume total bola dalam sel satuan	4/3π(0.5a)^3	4/3π((2^1/2)a/4)^3	4/3π((3^1/2)a/4)^3
7	Volume sel satuan	a3	a3/2	a3/4
8	Faktor tumpukan atom	0,52 atau 52%	0,68 atau 68%	0,74 atau 74%

 

Penjelasan dan penurunan data di table diatas

A.       A. Sc(SIMPLE CUBIC)

          Struktur dan spesifikasi Kristal terdapat dalam bentuk sederhana biasanya disebut dengan SC(Simple Cubic). Pada struktur SC ini terdapat 6 bilangan koordinasi.Bilangan koordinasi tersebut adalah Keadaan dimana sebuah atom dikelilingi oleh sejumlah atomatom yang terbanyak yang ada tepat disebelahnya menjadi dasar besar bilangan koordinasi suatu kisi sel .Kemudiam struktur SC ini dapat kita ketahui bahwa disepanjang sisi kubus akan ada atom atom yang terletak di bagian sudut saja dan akan bersinggungan mengakibatkan jumlah unit dari sel pada struktur hanya berjumlah 1(1/8 dari jumlah sudut). Dalam struktur ini terlihat bahwa atom-atom bersinggungan hanyalah disepanjang sisi kubus tersebut maka demikian masing-masing atom memiliki 6 atom tetangga yang terdekat yang posisinya berada dalam satu bidang.Faktor tumpukan atom nya 0,52=52%

A.      B. BCC(Body Centered-cubic)

          Suatu kisi yang berbentuk kubus dengan sisi-sisi sama panjang dimana ada 8 tempat atom pada masing-masing sudut dan 1 tempat atom di pusat kubus disebut kristal BCC. Menghitung atom tersebut dengan memandang atom sebagai bola yang bulat dengan pusat bola tepat berimpit dengan titik tempat atom berupa titik-titik perpotongan garis-garis rusuk maupun diagonal, yang khas didalam ruang tertentu. Jarak antara atom-atom yang terdekat yang saling berimpitan dipakai sebagai acuan menghitung panjang rusuk kubus atau panjang kisi sel yang disebut konstanta kisi atau parameter kisi a. Disini perlu dicatat, bahwa jari-jari atom diasumsikan sama panjang.Faktor tumpukan atom nya 0,68=68%

A.           c.  Fcc(Face centered-cubic)

            Dalam kisi FCC pusat bola-bola berimpit tepat pada masing-masing sudut  kubus dan pada pusat masing-masing keenam bidang muka kubus. Struktur FCC(face centered-cubic)ini terletak pada bagian sisi biasanya di bagi menjadi dua. Adapun total atom yang dimilki oleh struktur kubus FCC(face centered-cubic) ini ialah sebanyak 4 yag diperoleh dari penjumlahan seperdelapan yang timbul dari masing-masing atom yang terletak 8 dari sudut yang mana setengah bagian atomnya yang terletak  di enam permukaan sel.

 

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